Quoted type name not actually valid as base class

[rwbarton]

Mypy accepts the following program, but it's actually an error at runtime (even if the lines are reversed).

class A('B'): pass
class B: pass

Sort of similar to #686, but this bug probably has a simple local fix.

[gvanrossum]

Sounds like pretty low priority since as soon as you import that module it'll fail loudly.