detect buildout and add buildout eggs to sys.path

I am trying to add support for buildout based projects to jedi.

So far this seems to work. But I guess it isn't quite ready to merge yet.

A few questions:
* Can (and should) I use jedi.parser to do the parsing instead of using the ast module?
* Is it okay to write a test directly against _detect_buildout  or should tests be written on a higher abstraction level?

I don't like the fact that this one uses inside the exception catching mechanism. (Exceptions somewhere inside are just ignored and therefore we're creating space for bugs.

Just use:
try:
    with open(module_path, 'rb') as f:
        source = f.read()
except IOError:
    pass
else:
    p = Parser(common.source_to_unicode(source), module_path)