Fix for Pearrc on OSX

This pull request fixes issues reported on these tickets:

https://github.com/virtphp/virtphp/issues/10
https://github.com/virtphp/virtphp/issues/28

The issue is that when there was an existing .pearrc on OSX pear phar installation would fail, creating what looked like an empty /share/php folder which should have all of Pear folders. 

The solution is to move the .pearrc file during Pear's installation and then moving it back when done. 

This has been tested on OSX and Linux.