fix(MapWindow): unicode foes in read_into_memory() used by gitpython TCs

Drop Windows only codepath bypassing memory-mapping due to some leaks in
the past. 
Now Appveyor proves everything run ok.  
Additionally, this codepath had unicode problems on PY3. So deleting it,
fixes 2 TCs in gitpython:
+ TestRepo.test_file_handle_leaks()
+ TestObjDbPerformance.test_random_access()

See gitpython-developers/GitPython#525

smmap/mman.py

@@ -31,9 +31,9 @@ class WindowCursor(object):
     __slots__ = (
         '_manager',  # the manger keeping all file regions
         '_rlist',   # a regions list with regions for our file
-                    '_region',  # our current region or None
-                    '_ofs',     # relative offset from the actually mapped area to our start area
-                    '_size'     # maximum size we should provide
+        '_region',  # our current class:`MapRegion` or None
+        '_ofs',     # relative offset from the actually mapped area to our start area
+        '_size'     # maximum size we should provide
     )
 
     def __init__(self, manager=None, regions=None):
@@ -308,10 +308,14 @@ def _collect_lru_region(self, size):
             if 0, we try to free any available region
         :return: Amount of freed regions
 
-        **Note:** We don't raise exceptions anymore, in order to keep the system working, allowing temporary overallocation.
-        If the system runs out of memory, it will tell.
+        .. Note::
+            We don't raise exceptions anymore, in order to keep the system working, allowing temporary overallocation.
+            If the system runs out of memory, it will tell.
 
-        **todo:** implement a case where all unusued regions are discarded efficiently. Currently its only brute force"""
+        .. TODO::
+            implement a case where all unusued regions are discarded efficiently.
+            Currently its only brute force
+        """
         num_found = 0
         while (size == 0) or (self._memory_size + size > self._max_memory_size):
             lru_region = None

smmap/util.py

@@ -116,16 +116,13 @@ class MapRegion(object):
         '_size',  # cached size of our memory map
         '__weakref__'
     ]
-    _need_compat_layer = sys.version_info[0] < 3 and sys.version_info[1] < 6
+    _need_compat_layer = sys.version_info[:2] < (3, 6)
 
     if _need_compat_layer:
         __slots__.append('_mfb')        # mapped memory buffer to provide offset
     # END handle additional slot
 
     #{ Configuration
-    # Used for testing only. If True, all data will be loaded into memory at once.
-    # This makes sure no file handles will remain open.
-    _test_read_into_memory = False
     #} END configuration
 
     def __init__(self, path_or_fd, ofs, size, flags=0):
@@ -160,10 +157,7 @@ def __init__(self, path_or_fd, ofs, size, flags=0):
             # bark that the size is too large ... many extra file accesses because
             # if this ... argh !
             actual_size = min(os.fstat(fd).st_size - sizeofs, corrected_size)
-            if self._test_read_into_memory:
-                self._mf = self._read_into_memory(fd, ofs, actual_size)
-            else:
-                self._mf = mmap(fd, actual_size, **kwargs)
+            self._mf = mmap(fd, actual_size, **kwargs)
             # END handle memory mode
 
             self._size = len(self._mf)
@@ -179,19 +173,6 @@ def __init__(self, path_or_fd, ofs, size, flags=0):
         # We assume the first one to use us keeps us around
         self.increment_client_count()
 
-    def _read_into_memory(self, fd, offset, size):
-        """:return: string data as read from the given file descriptor, offset and size """
-        os.lseek(fd, offset, os.SEEK_SET)
-        mf = ''
-        bytes_todo = size
-        while bytes_todo:
-            chunk = 1024 * 1024
-            d = os.read(fd, chunk)
-            bytes_todo -= len(d)
-            mf += d
-        # END loop copy items
-        return mf
-
     def __repr__(self):
         return "MapRegion<%i, %i>" % (self._b, self.size())
 
@@ -243,6 +224,9 @@ def release(self):
         """Release all resources this instance might hold. Must only be called if there usage_count() is zero"""
         self._mf.close()
 
+    def __del__(self):
+        self.release()
+
     # re-define all methods which need offset adjustments in compatibility mode
     if _need_compat_layer:
         def size(self):
@@ -267,7 +251,7 @@ class MapRegionList(list):
     """List of MapRegion instances associating a path with a list of regions."""
     __slots__ = (
         '_path_or_fd',  # path or file descriptor which is mapped by all our regions
-        '_file_size'        # total size of the file we map
+        '_file_size'    # total size of the file we map
     )
 
     def __new__(cls, path):