Added custom IEqualityComparer to SpriteFont glyph dictionary.
Replaced internal _texture access.
Removed _characters in favor of auto-property.
Simplified logic around missing glyphs.
Removed always true if statement.
Merge pull request #2604 from SickheadGames/fonts

SpriteFont Optimizations Pt. 1
Don't stop the Stopwatch until we are ready to start the run loop. Previously we'd be accumulating update time while the game loaded, which would lead to _maxElapsedTime worth of updates before the first draw call was made.
Redo the IsRunningSlowly calculation to use a method that closer resembles XNA behaviour. We now count how many lost frames we've had and use that as the trigger.

Fixes #2595
Merge pull request #2607 from danzel/isrunningslowly

Redo the IsRunningSlowly calculation
Merge pull request #2606 from danzel/gamestart-update-spam

Fix burst of Game.Update calls at the start of the game
Fix referencing aliasing with new Protobuild
Fix build error under Windows
Merge pull request #2610 from hach-que/alias-fix

Fix referencing aliasing with new Protobuild