check window stack before sending events
This should fix FC on Android with "Start with last opened file" checked
fix cannot load thrift library on Android
update luajit-launcher
fix two finger pan gestures detection
This is a stupid bug I introduced when I thought 0 evaluated to be false.
Actually in Lua only explicit `false` and `nil` are evaluated to `false`
all other values are true in logical expressions.

This should also fix #546. Probably because the touch screens in Kindle
are not as sensitive as in Kobo, this problem is not discovered early
util I play with multi-touch on a Android phone which has a sensitive
enough screen to expose this bug.
Merge pull request #633 from chrox/master

fix two finger pan gestures detection