add priority sorting to $$resolve_depends()

all else being equal, items with a higher numerical priority will appear
first in the result.

Change-Id: I4ee37ff404a53c4152a1e4fc2fc3c23ef525234d
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
make module-by-module build work when old builds are installed

when doing a module-by-module build, we need to also use includes and
libraries from the install tree, as it contains the current module's
dependencies. but a pre-existing installation of the current module must
not be found first, as it would cause trouble latest when it was somehow
incompatible.

but purely topological sorting of the dependencies could cause the
locations to be mixed up. therefore we give modules which are part of
the current build a priority boost.

Change-Id: I8fdbb46f0a2a630781c8a2177468039c1122151a
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

Conflicts:
	mkspecs/features/qt_module_pris.prf
Merge pull request #13 from giucam/master

qmake fix to improve build stability of qtwayland