Complain if we don't load(qt_module) first

Complain if we don't load(qt_module) first

Not having load(qt_module) first in a .pro file which later
does a load(qt_module_config) will likely overwrite
compiler/linker options in the .pro file.

This can be hard to figure out, and wasn't required before
when we used a global .qmake.cache for all modules, since
it 'preloaded' qmodule.pri file for all .pro files.

Change-Id: I8a9aa3247f938be0b3b13f8c8cc96c18a142ba7b
Reviewed-on: http://codereview.qt.nokia.com/412
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>