Implementing "-n" flag

plus its prerequisite `Kernel.gets`
Implementing `Kernel.gets` loop in RPython and moving it to the right spot
Changes per feedback
Trying out a pre-built frame version of Kernel.gets loop
Merge remote-tracking branch 'upstream/master' into mbh/dash-n-flag-plus-Kernel#gets
Merge pull request #480 from modcloth/mbh/dash-n-flag-plus-Kernel#gets

Implementing "-n" flag