fix one of the possible causes of build failures

Update binding_of_caller to v0.7.1

Update contributing file with latest insights.

Updating this dependency fixed my Ruby 2.0 installation issues.

IMPORTANT! Data converting in migrations was wrong. Fixed

Fix project transfer error

update grape to 0.3.1 for ruby 2.0 support.

closes #2300

add grape-entity, that is split from grape 0.3.0.
remove usage of deprecated error_format, that is removed in grape 0.2.3.

Merge branch 'state-machine-stage-2' of https://github.com/Undev/gitlabhq into Undev-state-machine-stage-2

Conflicts:
	app/models/merge_request.rb

Show only ≤16 lines of codes in a discussion in a MR (issue #2860).