Trap SIGINT

[yfeldblum]

bin/bundle should trap SIGINT all the time, rather than just surrounding Bundler::CLI.start.

Currently, if the user hits <ctrl>+c generating a SIGINT while bundler is in the middle of require 'bundler'or require 'bundler/cli', the error will be unhandled. Bundler should trap this SIGINT too by wrapping the whole binary in an exception-handling block which handles Interrupt. If Bundler did so, then there would be much less chance (essentially just the binstub or any -r flags) for a SIGINT to go unhandled.