Merge changes from the libogg autogen.sh.

In particular, enable maintainer-mode by default, and use
a more direct test for the proper libtoolize executable
that works on recent MacOS X, whose 'which' doesn't set
an return code like the GNU version.


git-svn-id: http://svn.xiph.org/trunk/ao@9694 0101bb08-14d6-0310-b084-bc0e0c8e3800