VS Express solution support

It's somewhat inconvenient for some people to have to edit solutions
themselves that were made with non-express VS versions. Considering
that they are forward compatible (VS 2012 will open solutions with
VS Express 2010 headers) it may as well be in upstream for the sake
of access.
Proper log line for SteamGuard prompt

This probably should have been changed along with my initial
patch but I was looking for the smallest changeset. Sorry about that.
This makes it unambiguous and points to the auth command instead
of making it looks like it's prompting for direct input
Add required protobuf reference (see 56aa750)
Merge pull request #288 from Lagg/picky-fixes

Picky fixes - A couple non-critical (and one build breaker) fixes