Update rcheckin.md to make clear its distinction from checkin

As a new user reading the rcheckin description it was difficult for me to understand how it was different from a regular checkin until I went to that page and saw the note. So I suggest having a similar note on the rcheckin page too.
Update unshelve.md to clarify that a new branch will be created
update special-actions-in-commit-messages.md to fix broken link to rcheckin doc
Fix for #474
Failing unit test
Rework logic to not require the "action" keyword
Merge pull request #473 from irontoby/patch-3

update special-actions-in-commit-messages.md to fix broken link to rchec...
Merge pull request #472 from irontoby/patch-2

Update unshelve.md to clarify that a new branch will be created
Merge pull request #471 from irontoby/patch-1

Update rcheckin.md to make clear its distinction from checkin
Merge pull request #475 from git-tfs/issue_474

Fixes #474