[qt4-build-multilib.eclass] Install configs for qtchooser.
[qt5-build.eclass] Install configs for qtchooser.
[qmake-utils.eclass] eqmake4: always use Qt4's qmake.

Use direct path to Qt4 binary location, fallback to /usr/bin.
Merge pull request #83 from mgorny/qtchooser-configs