cmake: Added --HEAD
python_helper prepends PYTHONPATH

…instead of appending. This should be safer against any
malformed user-defined values in the PYTHONPATH.
For brewed python, make sure to unset the PYTHONPATH

during building of python software inside of a `python do … end` block.
Python: Exit if PYTHONPATH is wrong

In our sitecustomize.py we instruct python to exit with an error message
if the PYTHONPATH is pointing to a wrong homebrew site-packages dir.
With wrong meaning another major python version.

If you set the PYTHONPATH to include
    $(brew --prefix)/lib/python2.7/site-packages
and start python3, it may pick up modules from there, wich can result
in errors for non pure python modules (such as PyQt).
Improve docs for Formula#python (python_helper)
Don't hard-code PYTHONPATH for `brew test`

This rules out any possibility to test Python 3.x software as the
PYTHONPATH is used by any Python and `brew test pyqt --with-python3`
fails because it picks up the `pyqt` module fomr Python 2.x's
site-packages. Upstream tells us not to set the PYTHONPATH and then
starting another (major) python version.
sip: We don't need sip and sip3 binaries

They are both identical. Difference lies in the config and libs.
qt: Default to build in-place and preserve the src

Needed for debug symbols.
PySide needs the source for documentation generation.
Closes #20020
qt: typo
qt: Fix Framework symlinks

doh.
qt5: Default to build in-place and preserve the src

Needed for debug symbols.
PySide needs the source for documentation generation.
Closes #20020
shiboken: 1.2.0, fix tests, run tests, add --HEAD
python: setuptools 0.9.8
python3: setuptools 0.9.8
python: Harden build by unsetting PYTHONPATH
python3: Harden build by unsetting PYTHONPATH
python3: reuse PythonInstalled better

We can use `PythonInstalled#binary`.
typo fix.
pyqt: Use the new configure-ng and improve python2/3

Improve handling of conflicting files (between 2.x and 3.x).
If only installing for one of these two versions, there is no conflict
to handle.

Update the test code to work with both python versions.

Indentation fix.
pyqt5: Improve test
pyside: 1.2.0, --HEAD

Needed a patch fix moc_qpytextobject.cxx not found
(https://codereview.qt-project.org/62479).

use `include` for `ALTERNATE_QT_INCLUDE_DIR`.

Point to Qt src dir.