FlxTrail bugfixes and changes

- Made solid public like it should be
- Removed reference to _solid which doesn't exist anymore
- Only change the solidness of newly created trailsprites
Merge pull request #319 from Gama11/dev

FlxTrail bugfixes and changes
Improved error log for invalid keys

- pressed() in FlxInputStates now also calls FlxG.log()
- the Key string is now logged as well, making the error log more
helpful
- the error log also covers the possiblity of the key being invalid
without being a function or number key
commit for issue #298 (moving calcFrame() calls in FlxText to draw() method)
Merge pull request #320 from Gama11/dev

Improved error log for invalid keys