v.to.rast: Give verbose message about number for all types

[wenzeslaus]

When there are no areas in the vector map, v.to.rast gave warning. After #2459, it gives a verbose message about number of selected areas when areas are selected as type. This gives the verbose message for all types when they are selected making the behavior more consistent across types (points, lines, boundaries, and centroids).

The default for type is point, line, and area, so three verbose messages are produced (when verbose output is enabled) for any vector map. (For the original version PR - as an alternative to #2459 with warnings consistent with the behavior before #2459 - a common vector map with a single type (point, line, or area) and the default parameters would produce two warnings.)

[wenzeslaus]

This PR addresses point 2 from #2459 by adding warnings for other types instead of removing the one for areas as #2459 does.

The types with this PR behave consistently resulting always in two warnings in the example cases.

Examples before

Points without this PR result in one warning:

$ v.to.rast input=bridges@PERMANENT output=bridges use=val
WARNING: No areas selected from vector map <bridges@PERMANENT>
Reading features...
...
v.to.rast complete.

Areas without this PR result in no warning:

$ v.to.rast input=nc_state@PERMANENT output=boundary use=val
Reading areas...
...
v.to.rast complete.

Examples after

Points with this PR result in two warnings:

$ v.to.rast input=bridges@PERMANENT output=bridges use=val
WARNING: No areas selected from vector map <bridges@PERMANENT>
WARNING: No lines selected from vector map <bridges@PERMANENT>
Reading features...
...
v.to.rast complete.

Areas with this PR result in two warnings:

$ v.to.rast input=nc_state@PERMANENT output=boundary use=val
WARNING: No points selected from vector map <nc_state@PERMANENT>
WARNING: No lines selected from vector map <nc_state@PERMANENT>
Reading areas...
...
v.to.rast complete.

[wenzeslaus]

This is still somewhat valid even after #2459 was merged because the warnings can be turned into verbose messages and than it would be very consistent across types even with verbose.

[wenzeslaus]

v.to.rast now give consistent verbose message about number for all features for all types. The PR is ready for review.

[echoix]

@wenzeslaus I'll let you merge, so you can adapt the commit message, as the first commit was close to the original description of this PR (using warning), but changed just now. It'll make more sense if you do it