* add error_details field to Build model and display build error on build parts screen

Conflicts:
	app/models/build.rb
	db/schema.rb
fix indentation
Fix two little nits:

* "none" -> "non" spelling
* use .present? instead of !.empty?
Merge pull request #36 from square/jcb/fix-nits-in-partition-error-code

Fix two little nits in partition error code
Fix race condition between saving a build and running a partition
job before the build is committed.
Merge pull request #39 from square/fix-partition-race-condition

Fix race condition between saving a build and running a partition
Include a link to the build SHA webhook.
Merge pull request #40 from square/web-hook-link

Include a link to the build SHA webhook.
Support POST with payload for webhooks plugin
Put therubyracer in the Gemfile

therubyracer is a JS runtime required by execjs, which is in turn required
by uglifier. therubyracer is not the fastest option but it is the most portable.

Doing this makes Kochiku easier to use by newcomers because they do not
need to install Node or another JS runtime on their machines.
Allow disabling kochiku merges on a repo by repo basis.

Controlled by a new column on Repository 'allows_kochiku_merges'.
Rename build auto_merge attribute to merge_on_success
Rename the AutoMergeMailer to MergeMailer
Rename GitAutomerge to GitMergeExecutor
Merge remote-tracking branch 'origin/disable-merge-for-repositories-option'

R: jkingdon
Change .ruby-version to 2.1.0
Switch to a fork of resque-retry to eliminate deprecation
bundle update for rails 4
update gems and configs for Rails 4
Address deprecated AR syntax