Adopt the same versioning scheme as other xfce packages

(Old svn revision: 28119)

configure.ac.in

@@ -3,7 +3,12 @@ dnl
 dnl xfwm4 - window manager for the Xfce4 desktop environment
 dnl
 
-m4_define([xfwm4_version], [4.5.90])
+m4_define([xfwm4_version_major], [4])
+m4_define([xfwm4_version_minor], [5])
+m4_define([xfwm4_version_micro], [91])
+m4_define([xfwm4_version_build], [r@REVISION@])
+m4_define([xfwm4_version_tag],   [svn])
+m4_define([xfwm4_version], [xfwm4_version_major().xfwm4_version_minor().xfwm4_version_micro()ifelse(xfwm4_version_tag(), [svn], [xfwm4_version_tag()-xfwm4_version_build()], [xfwm4_version_tag()])])
 
 m4_define([gtk_minimum_version], [2.6.0])
 m4_define([xfce_minimum_version], [4.5.90])