For maintainers, add a bunch of flags to the GCC compilation line to flag more warnings about our constructs.
For maintainers, add a bunch of flags to the GCC compilation line to flag
more warnings about our constructs.

* configure.ac:
  (CFLAGS): add flags when --enable-maintainer-mode is specified

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion