For W32 use a build number instead of abbreviated commit id.

For W32 use a build number instead of abbreviated commit id.

We would need to use a shortened commit id so that it fits into an 16
bit Windows variable.  Further it is a random number and not something
increasing.  Thus a build number made up from the day of the year and
the hour is much more useful to describe a build number for a specific
revision.
* configure.ac [W32]: Replace BUILD_REVISION by BUILD_NUMBER.
* src/versioninfo.rc.in: Ditto.