brew-pull: run git am --abort on failure.

Library/Contributions/cmd/brew-pull.rb

@@ -48,7 +48,7 @@ ARGV.named.each do|arg|
   revision = `git rev-parse --short HEAD`.strip
 
   ohai 'Applying patch'
-  patch_args = ['am']
+  patch_args = []
   patch_args << '--signoff' unless ARGV.include? '--clean'
   # Normally we don't want whitespace errors, but squashing them can break
   # patches so an option is provided to skip this step.
@@ -59,7 +59,12 @@ ARGV.named.each do|arg|
   end
   patch_args << patchpath
 
-  safe_system 'git', *patch_args
+  begin
+    safe_system 'git', 'am', *patch_args
+  rescue => e
+    system 'git', 'am', '--abort'
+    odie 'Patch failed to apply: aborted.'
+  end
 
   issue = arg.to_i > 0 ? arg.to_i : url_match[4]
   if issue and not ARGV.include? '--clean'