Make sure gcc_selected() returns something useful on Xcode 5.

On Xcode 5, /usr/bin/gcc is no longer a symlink but actually clang.
This causes Fink::Services::gcc_selected() to return "0" which prevents
fink from installing. It would also break installing packages with a
GCC field. This patch always returns "4.2" when gcc is clang.
Extrapolate Xcode versions for future releases
Updated supported Xcode versions.
Merge pull request #87 from akhansen/fix-xcode5-bootstrap

Fix supported Xcode versions for bootstrap using Xcode 5 on 10.8
Merge pull request #85 from danielj7/xcode-5-fix

Make sure gcc_selected() returns something useful on Xcode 5.
Comment that hardcoded "4.2" return value in gcc_selected() is for compatibility with enforce_gcc().
Merge parts of selfupdate-git2 branch
Update bundled docs for 0.35.2 release.
Update with 0.35.2 features and 0.36.x plan.
Forbid PYTHONPATH in RuntimeVars (https://github.com/fink/fink/issues/88)
pkgs: add expat1 2.1.0-1, needed by gettext-tools

We didn't need this before because previously we did
not actually build gettext-tools during bootstrap.
But the new dpkg depends on gettext-tools, so now we
do need it.
pkgs: add libncursesw5 5.9-20110507, needed by new dselect

Since dselect is a splitoff of the dpkg package that is
NOT essential, we don't make libncursesw5 essential either.
pkgs: add xz 5.0.5-2, needed by new dpkg

We need this as dpkg links against liblzma and the .deb format itself
will move to this compression format in the future.
pkgs: make xz essential
pkgs: add time-date-pm 1.16-1, needed by new dpkg
pkgs: make time-date-pm essential
pkgs: add objtools 2.22-3, needed by new dpkg

This is used for the new "automatic dependencies" code
pkgs: make objtools essential
pkgs: fix objtools to work in both 10.7 and 10.4 dists.
pkgs: add texinfo 5.1-2