Add a new formula for PSPP

PSPP is the GNU reimplementation of SPSS, a package for doing
statistical analysis. This formula adds support for the GUI and
command-line pspp tools.
Minor flag and style fixes for PSPP formula

Make running tests default. Remove unneeded compile flags. Fix
formatting.
Change cairo to a hard dependency

GUI and command line builds now need cairo and pango
Move the disable postgres flag

For now, move it into the unconditional arguments until I add postgres
support
Remove unneeded PKG_CONFIG_PATH tweaks

Looks like everything works now even without manipulating the
PKG_CONFIG_PATH
Remove clang checks

Builds fine after a fresh reinstall