lua: always handle key repeat on the script side

Simpler, and leaves the decision to repeat or not fully to the script
(instead of requiring the user to care about it when remapping a script
binding).
lua: remove redundant call
input: simplify
travis: add gcc to the build matrix

For the purpose of running Coverity correctly.

Although I'm not sure how well this works. gcc won't work on OSX, and
also I'm not sure if Coverity will act up if the build matrix has more
than 1 configuration (will it submit multiple scans?).