Update pcl.rb

Edited to update to vtk5 and pcl-1.7.1.  This is a HEAD-only fix at the moment, the stable version fails for some reason.

I've included optional arguments for unit tests/examples and a check for sphinx-build.  Also pcl apps are now prefixed 'pcl_foo', so updated the test.

Checked on 10.8.4 and will check on a 10.8.5 system later. :)