Disable atsign-inbounds when running tests on Travis

Also propagate the `--check-bounds` option to workers
What would you suggest? Should I keep track of the arguments that should be propagated to workers in `repl.c` instead? Or leave Base alone, and just set `exeflags=ˋ--check-bounds=yesˋ` when calling `addprocs` from `runtests.jl`?