Detect when libtoolize is called glibtoolize.

It's the case on Darwin, and might be in other BSDs as well.
As referred in #268.
Supersedes PR #269.

autogen.sh

 #!/bin/sh
 
+if glibtoolize --version &> /dev/null
+then libtoolize=glibtoolize
+else libtoolize=libtoolize
+fi
+
 aclocal -I m4
 autoconf
 autoheader
-libtoolize --copy --force
+$libtoolize --copy --force
 automake --add-missing --copy
 
-