The :wa command now considers projection buffers

The :wa command implementation wasn't considering the possibility that
an ITextBuffer was actually an IProjectionBuffer instance.  Hence in
situations like .cshtml files it couldn't find a backing ITextDocument
and believed the file to not be dirty when it in fact was.

closes #1143
Respect VS incremental search

The previous attempt at detecting the new incremental search UI for VS
2012 wasn't a complete success.  It turns out that the UI will receive
keyboard input even when it doesn't have keyboard focus in a few
scenarios.  The new code simply detects it's visibility and keys off of
that

closes #1109