- Reorganized stuff in configure.in and added a few comments

# This isn't nearly as big a change as the diff would lead one to believe.
# I've tested this on all my machines and its working for sniper too.
- Added a check for ApplicationServices/ApplicationServices.h (Mac OS X)
- Added AC_PROG_CPP, AC_PROG_CXX and AC_PROG_CXXCPP
# (the bundled libmysql build was failing without them with ac2.52/OSX)
- Improved the IPv6 check to fail on Mac OS X (there's no IPv6 there yet)

Author: Marko Karppinen