git revision tagging

[Brian J. Tarricone]

Hi guys,

So we talked about this a bit before, and I think the way we were going
was to leave out date and ordering information in the revision tagging.
 So for packages built from git, we'll just use the package name,
previous released version, the string 'git-', and then the first 8
characters of the commit SHA1.  For example:

xfdesktop-4.7.2git-82f1bc94

Shell code for autogen.sh:

if [ -d .git ]; then
  revision=$(git rev-parse HEAD | cut -c1-8)
fi
if [ -z "$revision" ]; then
  revision=UNKNOWN
fi

Of course, if people want to do something different for /apps/,
/panel-plugins/, etc., that's your choice, but everything under /xfce/
should use this scheme to be consistent.

	-brian