.gitignore: add coverage/ subdirectory
tag Guard.setup_signal_traps spec as slow

This allows these examples to be excluded via

  rspec -t ~speed:slow
include guard-rspec in test group environment since it's required by guard_spec.rb

This fixes the breakage introduced by 613b11d into Travis builds.
fix indentation
Revert silent discard of NoMethodError from plugins introduced by 95d9cd1b (fixes #413)

Rather than silently discarding all NoMethodErrors, we just check
whether the plugin implements the task and only execute it if it does.
fix typo
refactor invocation of tmux client
prevent tmux output from messing up spec output
Merge pull request #414 from aspiers/master

misc fixes