Added parsing of dictionary comprehension
Added parsing of set comprehension
Added semantic analysis for set comprehension
Added type checking for set comprehension
Added semantic analysis for dictionary comprehension
Factored out common code
Added test for type checking of dictionary comprehension
Added type checking for dictionary comprehensions
Factored out common code
Merge branch 'master' into dict_comp

Conflicts:
	mypy/parse.py
	mypy/semanal.py
	mypy/treetransform.py
Merge branch 'dict_comp' of https://github.com/spkersten/mypy into spkersten-dict_comp
Merge branch 'spkersten-dict_comp'
PEP 8 fixes