Allow "-h" or "--help" to get general help.
Allow "-h" or "--help" to get general help.

These don't really fit into our syntax, but because of the "default
command" feature, people would get surprising output for them
if they were not supported (namely, the build-specific help).

Change-Id: I50dc69679803aaeec5937fbf5f8df492f1928180
Reviewed-by: Joerg Bornemann <47777b9406dbddd02a3fdca8341789a013805a11@digia.com>

villytiger/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,Distrotech/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,villytiger/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,villytiger/qbs,gatzka/qt-labs-qbs,villytiger/qbs,Distrotech/qbs,gatzka/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,Distrotech/qbs,qtproject/qt-labs-qbs,gatzka/qt-labs-qbs,qt-labs/qbs,Distrotech/qbs,qt-labs/qbs,villytiger/qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,gatzka/qt-labs-qbs,Distrotech/qbs,Distrotech/qbs,Distrotech/qbs,villytiger/qbs