Commit Lawrence D'Anna's patch to change

Commit Lawrence D'Anna's patch to change
SetOututFileHandle to work with IOBase.

I did make one change after checking with Larry --
I renamed SBDebugger::Flush to FlushDebuggerOutputHandles
and added a short docstring to the .i file to make it
a little clearer under which context programs may need
to use this API.

Differential Revision: https://reviews.llvm.org/D38829

llvm-svn: 317180