Use nose-timelimit with travis to help find slow tests.
Remove opt that isn't used.

This fix the scan test_rop tests! next commit will fix the random opt problem.
remove the EQ opt in a EQ opt. This is useless as the outer opt had only 1 inner opt.
Have deterministic optimization order.
Make opt name used more explicit.
Merge pull request #1804 from nouiz/fix_scan_mem

[BUG Fix scan mem optimization