Changes in order to build a .app with current version of CellProfiler.

I needed to upgrade py2app. The error message I got with the old
version was "error: cannot copy tree
'/Users/ljosa/src/CellProfiler/cellprofiler/utilities/js.jar': not a
directory". According to
https://bitbucket.org/ronaldoussoren/py2app/issue/49/a-non-python-file-inside-python-package,
this happens because py2app treats the jar as a zip file. This was
fixed in py2app on or before 2012-10-10. The version of py2app I ended
up installing was 0.7.3.

Next, I had to change "./icons" to "icons" in OPTIONS['packages']
because py2app no longer tolerates dots in the package names (because
it doesn't tolerate subpackages). See
https://bitbucket.org/ronaldoussoren/py2app/commits/d2b3d778a5ebc3c5f30106cc532a368d405f5dfc.

Finally, I had to remove imagej from OPTIONS['excludes'].

CPA now builds with the multiprocessing branch of
CellProfiler (26c3bcd302f053a84a152fb4cf70d5b379f90ffc).