casacore: Fix compiler and refactor

Add HEAD url. Suppress the latest Lion clang in favour of lvm-gcc.
Refactor system commands to use FileUtils methods instead. Specify
the CASA data directory (which will be currently be provided by user).
New formula: casacore-data

This provides the meta-data needed by the casacore Measures module
such as leap second tables, observatory locations and Solar System
ephemerides. It downloads the latest measures_data tarball from the
ATNF FTP site (updated weekly). Alternatively it can link to the
data directory contained in the NRAO CASA application (aka casapy).
The casacore package looks in /usr/local/share/casacore/data for
the metadata.
casacore 1.5.0

Update to latest version. Allow parallel compilation so that the
package installs in a third of the time. Remove patches that are no
longer required in the new version.
casacore: Depend on casacore-data + test

Now pull casacore metadata in as a dependency to ensure that tests and
other programs built on casacore will work as expected. Add a simple
test that checks for the presence of metadata.