Pass tarname argument to AC_INIT
If AC_INIT is invoked without tarname argument PACKAGE_TARNAME and
PACKAGE will be sanitized (lowercased, and all characters other than
alphanumerics and underscores are changed to ‘-’.)
For windowmaker this has the sideeffect of changing install directories,
util/wmaker.inst installs stuff to #pkgdatadir# which suddenly is
/usr/share/windowmaker instead of /usr/share/WindowMaker.
Supplement AC_INIT invokation with tarname (and while we are at it url)
argument to fix this.