Correctly print version number
In
4a3e83d7f59760dd7ffb936810f6df9e95ccd1dc (switch to automake/libtool),
some names of macros were changed, but not carried through completey,
which resulted in "cloog -v" printing bogus information, as reported
by Cedric Bastoul.
This fixes the problem and adds a cloog_version() function that
returns a printable version string, including information about
the currect git version. The CLOOG_RELEASE and CLOOG_VERSION
defines are removed from cloog.h since they are both strings
and cannot be used for numerical comparisons anyway.