Add net.sln output folders to .gitignore.

Add net.sln output folders to .gitignore.

BUG=none
TEST=none

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=75439

[Jói, 2011-02-18 19:54:35]

src/net is a separate module (as is src/base) so it has its own net/net.sln file
that you can open instead of the full chrome/chrome.sln file. When you do that
and build, you get net/Debug or net/Release, so adding those to .gitignore or
git thinks they're new files that should maybe be tracked.

[Roger Tawa OOO till Jul 10th, 2011-02-18 21:19:15]

lgtm