Add an initial cache file for CMake to use at build-time.
Provide a cache file with additional CMake commands that CMake reads when
bootstrapping. For now it just sets the BUILD_TESTING cache variable to OFF,
so that most tests are not processed when building the port.
Building the tests was particularly troublesome in Qt 4's case: since we
have separate ports for each part, one could have devel/qmake-qt4 installed
and not, say, devel/qt4-corelib, which would make CMake fail.
See https://mail.kde.org/pipermail/kde-freebsd/2013-July/015703.html for an
No PORTREVISION bump since package creation was not broken.