configure: CentOS 6.5's git-archive cannot create a tar.gz

Signed-off-by: Euan Harris <euan.harris@citrix.com>
configure: Use the correct path when clearing out SOURCES

Signed-off-by: Euan Harris <euan.harris@citrix.com>
configure: Use number of commits as repository version if no tags are found

Signed-off-by: Euan Harris <euan.harris@citrix.com>