[#1923] Replaced GNU find/xargs combo with portable find invocation.

Why?
--------

 The one liner from paver.sh for cleaning pyc files does not work on AIX.

 Here is the error
```
$ find . -name '*.pyc' -print0 | xargs -0 -r rm

xargs: unknown option: 0
Usage: xargs [-p][-t] [-e[EndOfFileString]] [-E EndOfFileString]
[-I ReplacementString] [-i[ReplacementString]] [-L Number]
[-l[Number]] [-n Number [-x]] [-s Size] [Command [Argument ...]]
xargs: unknown option: r
Usage: xargs [-p][-t] [-e[EndOfFileString]] [-E EndOfFileString]
[-I ReplacementString] [-i[ReplacementString]] [-L Number]
[-l[Number]] [-n Number [-x]] [-s Size] [Command [Argument ...]]
find: bad option -print0
```

Solution?
-------------

Replace the find/xargs combo that makes use of the GNU extensions with a more portable invocation that uses `-exec +`


How to check?
---------------------

Please review the changes. Test the command in both AIX and Linux with a directory containing:
```
./-2.pyc
./1 2 3.pyc
./1.pyc
```

Reviewers: @adiroiban