Add sdk/ prefix to Firefox/lib/main.js require()s
Changes for recent versions of Jetpack
Reimplement makelinks.sh as a wrapper around makelinks.bat

makelinks.bat had several issues (bashisms with #!/bin/sh, incorrect handling
of .user.js files etc.)

Rather than keep a second version in sync with the .bat file that seems
better-maintained, this commit rewrites the whole thing to read the .bat and
mimic its behaviour.
Add Makefile and browser-neutral configuration

Note: this replaces makelinks.sh
Add example test architecture