[oe] PREFERRED_PROVIDER and RDEPENDS

[Björn Krombholz]

qt4-x11-free and qt4-x11-free-gles both provide qt4-x11-free.

Setting

PREFERRED_PROVIDER_qt4-x11-free = "qt4-x11-free-gles"

works as expected. When you bitbake qt4-x11-free you will get the -gles variant.

On the other hand, when bitbaking task-qt4-x11 which RDEPENDS
on qt4-x11-free it is trying to build qt4-x11-free.bb and not the -gles recipe.

Is this a general bug? Or would the correct way be adding something like
RPROVIDES += "virtual/qt4-x11"
to qt4-x11-free.inc and changing the RDEPENDS to the virtual package?