These days the extra vlc revision is an integer (1.1.10.1), not a
letter like in 0.8.6f days
Make PACKAGE_VERSION_* be integer, we don't need them to be strings
PACKAGE_VERSION_EXTRA now represents only this number, and is set to
0 when not used (1.1.11.0 represents 1.1.11)

Add PACKAGE_VERSION_DEV (== "git" or "rc*"), to be sure development
versions are less recent than released versions.
This string is never displayed, it is only tested for nullity

The file format on our servers can use X.Y.Z or X.Y.Z.E