Fix Python dependencies

In the wake of Homebrew PR 24842 all Python support reverts to the
old brew approach. No more python object supplying the version,
site-packages dir etc. These are now figured out directly in each
formula. The check for Python package dependencies has also reverted,
and there is in general no need to depend on :python (as it is always
available on Mac OS X anyway).
obit: Fix X11 support

For some reason the ObitView configure script picks up X11 correctly but
then does not set the include directory correctly, leading to X11 headers
not being found. Point to them explicitly using pkg-config.
casacore: Update clang support

The stable release is still broken with the latest clang version.
Force clang on Mavericks to use the old gcc-based libstdc++ instead of
the swankier libc++ for now, as there are clashes involving the
std::complex type during compilation.
casarest: Disable clang and patches for now

The latest clang still does not like the GCC extensions in use (e.g.
variable-length arrays). This will need some actual code fixes as
everyone should use clang on Homebrew.

Hard-code libstdc++ to avoid compiler clashes on clang. Ignore the
patches for now as they seem to be obsolete on the stable version
as well (?).