[#1925] Add hack to avoid AIX's find error when nothing matches.

Why?
--------

There is an error on AIX if no pyc files are to be removed by Brink's `paver.sh`:
```
-bash-3.2$ find ./ -name '*.pyc' -exec rm {} +
-bash-3.2$ find ./ -name '*.pyc' -exec rm {} +
find: 0652-083 Cannot execute :: A file or directory in the path name does not exist.
```

Solution?
-------------

Unfortunately, this looks like an inconsistent behaviour from AIX's `find` command. I can't reproduce this on Linux and I can't reproduce this in AIX with `\;` instead of `+.` So I would conclude this is an obscure AIX bug. However, testing shows it is present in both AIX 5.3 (where the + feature was first introduced) and 7.1.

Google returns very few results for this error code and only one with + as final parameter: ​https://www.ibm.com/developerworks/community/forums/html/topic?id=77777777-0000-0000-0000-000014414114.

I've added a lil' dirty hack on AIX and we create an empty .pyc file just before calling `find`, so that it will always find something.


How to check?
---------------------

Please review the changes. Test the `paver.sh` script in AIX with no files to be found.

reviewers: @adiroiban