Insert the Qt major version (5) in the library names

Insert the Qt major version (5) in the library names

As discussed on the mailing list, insert the Qt major library version in
the library name, so even the development files can be co-installed with
Qt 4.

Discussed-on: http://lists.qt-project.org/pipermail/development/2012-September/006545.html
Discussed-on: http://lists.qt-project.org/pipermail/development/2012-September/006551.html
Change-Id: If0be11ebf9454a9fb6d96cda161790dfd53c00f5
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>