Prevent early interrupt from displaying stack trace

If a user pressed Ctrl-C _really_ early in a hook run, they would get an
ugly stack trace since we don't set up a signal handler until we load
the Overcommit code.

Add a signal handler so that these early interrupts can be gracefully
caught.

Change-Id: I184cdcb3a76802095508d33af01b63f694cfbb83
Reviewed-on: http://gerrit.causes.com/41195
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

CHANGELOG.md

@@ -10,6 +10,8 @@
 * Handle edge case where if a file was created in the working directory by a
   separate process in between the working tree being reset and the stash being
   applied, the hook runner would silently fail
+* Prevent stack traces from appearing during early interrupt before Overcommit
+  has loaded its code
 
 ## 0.15.0
 

template-dir/hooks/overcommit-hook

@@ -4,6 +4,14 @@
 # in all of your git hooks being symlinked to this file, allowing the framework
 # to manage your hooks for you.
 
+# Prevent a Ruby stack trace from appearing when we interrupt the hook.
+# Note that this will be overridden when Overcommit is loaded, since the
+# InterruptHandler will redefine the trap at that time.
+Signal.trap('INT') do
+  puts 'Hook run interrupted'
+  exit 130
+end
+
 # Required for Ruby 1.8 compatibility (for older OSX versions)
 if RUBY_VERSION.split('.')[0..1] == %w[1 8]
   require 'rubygems'
@@ -84,7 +92,7 @@ rescue Overcommit::Exceptions::HookSetupFailed,
   exit 74 # EX_IOERR
 rescue Overcommit::Exceptions::HookCancelled
   puts 'You cancelled the hook run'
-  exit 1
+  exit 130 # Ctrl-C cancel
 rescue Overcommit::Exceptions::InvalidGitRepo => error
   puts error
   exit 64 # EX_USAGE