[Development] api changes

[Girish Ramakrishnan]

Hi,
I am going through all the new apis. I have a couple of more changes
to the public apis already. I am not submitting them to api_changes
branch. I think Lars and co are having enough trouble as-is with
getting api_changes to merge to master :-) All the commits will have
the "api:" prefix in the commit message (so it's easy to see on my
dashboard). I will stage them only after api_changes is merged.

My current understanding of the "qpa" plan is this, correct me if I am wrong:
1. Files with _qpa in them are supposed to be used by plugins and
plugins only. If you see, _qpa.h being used in application code, they
are using a binary and source incompatible Qt. _qpa.h also lacks the
'we mean it' header which I will add.
2. No public Qt include files should have _qpa.h in them
3. _qpa.h files are installed only so that we can allow development of
plugins outside of qt source. I would like to see them not getting
installed at all but I don't know if this is an oversight or
intentional.
4. Also, I would like to see all the handle() functions in public api
die. Or make them protected and make all the classes friends (as such
they are all mostly friends anyway). handle() encourages writing
binary incompatible code in userland. Note that handle() in qpa land
is very different from handle() in the old qt4 land (where it just
implied being binary compatible but platform specific).

Thanks,
Girish