Add doctor check for OS X > 10.8
Recognize OS X 10.9 and Xcode 5.0

Closes #20410.
Closes #20401.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
sqlite: style nit
vim: Add descr. for adding LDFLAGS.
libxml2: Added --HEAD and fixed Python bindings

-  Python 2.7+ is needed for current version. A fix to
   build with Python 2.6 has been recently added to
   the master:
   https://git.gnome.org/browse/libxml2/commit/?id=722923bc9b788f028e4221c77138fc66735a3113

-  So for system python on 10.6, you'll have to use
   the --HEAD for now.

-  Fix audit not detecting the `if python` after
   the def caveats.
zsh-syntax-highlighting: fix typo in caveats
zeromq: remove Java notes from caveats
zabbix: remove caveats

Documentation is easily found via brew home zabbix
z: remove back-compat caveats
vpnc: remove caveat that duplicates option text