phive.xml always updated

[kingcrunch]

I want to create a Makefile, but even phive install updates phive.xml on every run. This means from makes point of view the tools are always expired. Since there is no lock file (see #92 ) phive.xmls timestamp should not change, when the file itself does not change.

[theseer]

The install command currently does not check whether the symlink in the tools directory is already present/points to the requested version but merely (re-)creates it.

As a result, the phive.xml gets "updated" - even though nothing actually changed from a content perspective.