Bugfixes

Fixes for a large number of bugs, some of which are newly found, some of which have been discussed before.

I tried to keep breaking-changes to a minimum; the major breaking change is in commit https://github.com/BlueRaja/SteamBot/commit/5f3ed9f1f24c01e0cd1097beb47cf9a856e7e1c7 - unfortunately, it's an extremely critical bug.  It might require some existing bots to change some `int`s to `long`s.

I've added more comments to the individual commits.