Fixed Menu search compatibility with Qt 4.6.
Fixed Menu search compatibility with Qt 4.6.

We were using the QLineEdit.setPlaceHolderText() method which didn't exist until Qt 4.7.

davidsminor/gaffer,hradec/gaffer,johnhaddon/gaffer,hradec/gaffer,cedriclaunay/gaffer,ImageEngine/gaffer,ImageEngine/gaffer,appleseedhq/gaffer,davidsminor/gaffer,johnhaddon/gaffer,ImageEngine/gaffer,cedriclaunay/gaffer,paulondc/gaffer,lucienfostier/gaffer,chippey/gaffer,ivanimanishi/gaffer,davidsminor/gaffer,GafferHQ/gaffer,goddardl/gaffer,GafferHQ/gaffer,paulondc/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,davidsminor/gaffer,goddardl/gaffer,chippey/gaffer,appleseedhq/gaffer,appleseedhq/gaffer,goddardl/gaffer,chippey/gaffer,cedriclaunay/gaffer,appleseedhq/gaffer,andrewkaufman/gaffer,paulondc/gaffer,ivanimanishi/gaffer,andrewkaufman/gaffer,boberfly/gaffer,paulondc/gaffer,ImageEngine/gaffer,chippey/gaffer,GafferHQ/gaffer,hradec/gaffer,andrewkaufman/gaffer,johnhaddon/gaffer,GafferHQ/gaffer,hradec/gaffer,andrewkaufman/gaffer,lucienfostier/gaffer,johnhaddon/gaffer,boberfly/gaffer,johnhaddon/gaffer,goddardl/gaffer,hradec/gaffer,GafferHQ/gaffer,lucienfostier/gaffer,cedriclaunay/gaffer,ivanimanishi/gaffer,ivanimanishi/gaffer,boberfly/gaffer,boberfly/gaffer