Need a way to specify context for a URL

Currently, the context for qsTr() is ultimately derived from:

QFileInfo(url).baseName()

This is inadequate for frameworks, such as QML, where the basename need not be unique. The context for a qsTr in QML modules should be derived from the URI of the QML element in which it appears.

The above code is also horribly inefficient, since it creates an entire file engine where a simple string operation would suffice.