PyQt: Replace bsd.pyqt.mk with Uses/pyqt.mk.
In preparation for landing PyQt5 ports, generalize devel/py-qt4's
bsd.pyqt.mk and make it a proper file in Uses/.
Ports wishing to depend on PyQt4 ports can now do the following:
USES= pyqt:4 USE_PYQT= foo bar_build baz_run
Other changes include the renaming of the PYQT4_DIST variable to PYQT_DIST
and the introduction of the PYQT_SIPDIR plist substitution variable. The
rest of the contents of Uses/pyqt.mk are pretty much identical to what we
had in bsd.pyqt.mk with additional processing of USE_PYQT.
Even though this patch touches files in many different ports, the goal is
for it to be a no-op from an end-user perspective (so that the basic
infrastructure is landed before the other, riskier changes): no dependencies
have been changed, PyQt/SIP/QScintilla have not been upgraded and the plists
should remain exactly the same, since PYQT_SIPDIR currently contains the
same value that used to be hardcoded in the plists.
Huge thanks to Guido Falsi (madpilot@) for spearheading most of the work: he
took the initiative to work on PyQt5 and sent D2910 to Phabricator with the
original version of this patch. Tobias Berner (tcberner@gmail.com) later
applied it to kde@'s experimental area51 repositories and did some more work
on it.