Add autotools { autoconf, automake, libtool } as contribs.

Add autotools { autoconf, automake, libtool } as contribs.

Primarily necessary for OSX platform after Xcode 4.2.x, but also useful for
any platform which is missing or has obsolete versions.

1. add configure option: --enable-local-autotools
2. --enable-local-autotools is automatically TRUE when any of { autoconf, automake, libtool } are not found in path.
3. --enable-local-autotools causes contribs of { m4, autoconf, automake, lib tool } to be built
4. add m4 to contrib (prerequisite for autoconf)
5. add autoconf to contrib (prerequisite for automaker and many contribs)
6. add automake to contrib (prerequisite for many contribs)
7. add libtool to contrib (prerequisite for many contribs)
8. All contribs (except the autotools themselves) automatically mark autotools as a prerequisite.
9. $(AUTOTOOL_MODULES) is available if other non-contrib modules need to mark as prerequisite.
10. PATH is automatically prefixed with contrib/bin for all modules, all targets.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@4933 b64f7644-9d1e-0410-96f1-a4d463321fa5