[oe] Using QT_DIR_NAME; Correct way of flattening QT5 directory structure?

[Adam Lee]

My system only runs Qt5. Hence no need to have `qmake` and others in
`/usr/bin/qt5`.
I prefer to have them in `/usr/bin`.

JaMa's comment[1] seems to suggest that all it takes is setting
`QT_DIR_NAME` to an empty string.

With this, I get tonnes of QA errors because `FILES_` paths now
contain `//`, which is the right behavior
as per the manual[2].

For example:

   $ bitbake qttools -e | grep FILES_qttools-mkspecs
   # $FILES_qttools-mkspecs
   FILES_qttools-mkspecs="    /usr/lib//mkspecs "

And the corresponding error being this:

   WARNING: QA Issue: FILES variable for package qttools-mkspecs
   contains '//' which is invalid. Attempting to fix this but you should correct
   the metadata.
   [files-invalid]

The build system [seems to] successfully correct the issue, and I see
the files in the resulting rootfs.
That said, I am either doing something incorrect, or something has to be fixed.

[1] http://lists.openembedded.org/pipermail/openembedded-devel/2014-February/094232.html
[2] http://www.yoctoproject.org/docs/current/ref-manual/ref-manual.html#qa-issue-files-invalid