don't miss brief button clicks or other inputs

mouse clicks, scroll motions, key presses, and joystick motions that are
activated then de-activated very quickly are now active for at least one
logical frame, so that they are not missed.

Fixes #1048
Check for undefined tiles when validating map tiles

Fixes #1051

We were only checking for tile indexes that were out of the tileset's
bounds. This overlooked tiles that were in bounds, but had no
definition. This commit remedies that.
Merge pull request #1054 from dorkster/fixes

Check for undefined tiles when validating map tiles
Merge pull request #1052 from sudoman/fixes

don't miss brief button clicks or other inputs