Build scripts don't work with unicode paths

Reproduce: create a python file, name it 'tést.py' (the accent is important), insert 'print "hello world"', try to run it via build script. Sublime Console will say:

Traceback (most recent call last):

File "./sublime_plugin.py", line 337, in run_

  return self.run(**args)

File "./exec.py", line 130, in run

UnicodeEncodeError: 'ascii' codec can't encode character u'\xe4' in position 85: ordinal not in range(128)

Fix: