QDeclarativeEngine::addImportPath() does not work if the drive letter is in lowercase.

If I register an import path with a lower-case driver letter like this:

engine->addImportPath("c:/dev/qt-components/imports");

then QDeclarativeImportsPrivate::resolvedUri() might not resolve that correctly because \a dir_arg
might have a capital drive letter (which is correct, since that's what canonicalPath() will ensure).
Due to that the following condition fails:

        if (dir.startsWith(path)) {

The result is that resolvedUri might return a uri like this: C:.dev.qt-components.imports.Qt.labs.components.meego,
and ultimately QDeclarativeImportDatabase::importPlugin() will complain:

"Internal error: Plugin imported previously with different uri"

It should canonicalize all filepaths before they are stored in the QDeclarativeImportDatabase.
The attached patch is a suggested fix for the problem.