Make the editor accept quests in format 1.3 now.
Make SOLARUS_INSTALL_DESTINATION modifiable
Handle all input events every frame.  Fix #513

The problem was that all inputs would only be handled one input per
frame, causing them to queue up and continue to run if the controls were
released.
Merge pull request #516 from xethm55/master

Handle all input events every frame.  Fix #513
Merge pull request #515 from hasufell/master

Make SOLARUS_INSTALL_DESTINATION modifiable