Clear QCoreApplication::applicationFilePath cache if argv[0] changes.

This allows boosters to precreate Q*Application instances.

Change-Id: Ie2c1399b216d9cc996210e077fa6d42d24bf9b0e
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Cleanup freetype data in a thread-safe way

One less obvious part of this patch: the fontCache pointer in engineData was not
safe. It isn't safe to rely on pointer addresses to verify we're cleaning up the
right thing, as a sequence of malloc()/free()/malloc() can return the same
pointer, and nothing was cleaning up the dangling pointer in engineData.

With this, it is possible to safely drop OpenGL contexts in QtQuick under all
conditions with no possibility of crashes.

Done-with: Aaron Kennedy <aaron.kennedy@jollamobile.com>
Change-Id: I7b91384251593730124323a74737d41333a05f59
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>