Use shiboken, not generatorrunner as default generator when building Mobility

[Michael Schubert]

Issue:
When no generator (-DGENERATOR) is specificed, PySide Mobility tries to use generatorrunner by default. This yields a compilation error in both latest release and Git head:

$ cd pyside-mobility-0.2.3/QtMobility/Contacts && /usr/bin/generatorrunner --generatorSet=shiboken snip
/usr/bin/generatorrunner: Error loading generator-set plugin: shiboken_generator module not found.

$ cd pyside-mobility-0.2.3/QtMobility/Contacts && /usr/bin/generatorrunner --generatorSet=/usr/lib/libshiboken-python2.7.so snip
/usr/bin/generatorrunner: Error loading generator-set plugin: Cannot resolve symbol "getGenerators" in /usr/lib/libshiboken-python2.7.so: (/usr/lib/libshiboken-python2.7.so: undefined symbol: getGenerators)

Workaround:
add the -DGENERATOR=shiboken flag when calling CMAKE

Resolution:
use shiboken as default instead of generatorrunner