Sort build path candidates to make nesting detection work.

While trying to setup a Symfony project i constantly "lost" the whole buildpath after adding some require-dev entries for docs generation. 
After lots of trial and error and finally some debugging i realized DLTK BuildpathUtils threw an exception (i did not find in the log) about nested paths when adding new buildpath items.
This was reproducable by adding "require-dev":{"pear/log":"dev-master"} to composer.json.
My fix is to sort paths list in BuildPathManager.update method. This works for me, but i don't know how exactly handling of inclusion / exclusion patterns work and if this could be affected by the change...