Add Attributes formAction, formEncType, formMethod and formTarget

This resolves #2425.
Permit th  attribute
Fix typo in comment of jquery-bootstrap example
reactComponentExpect expects itself

This was a bug when reactComponentExpectInternal was separated from
the normal reactComponentExpect flow.
Use jest for `npm test`

I've given in and this is easier than `npm run jest`. `grunt test` still
exists and is used by Travis so this has no CI implications.
Merge pull request #2600 from zpao/npm-test

Use jest for `npm test`
Merge pull request #2596 from sebmarkbage/rce

reactComponentExpect expects itself
Merge pull request #2553 from mhuggins/headers-attribute

Permit th `headers` attribute
Update commonjs example for 0.12
Merge pull request #2610 from zpao/update-commonjs-example

Update commonjs example for 0.12
Monitoring code use of cloneWithProps
Merge pull request #2613 from jsfb/monitor-cloneWithProps

Monitoring code use of cloneWithProps
Add top-level API docs section for React.createElement.
Adding link to wiki

Based on conversation in https://github.com/facebook/react/pull/2501. A good place to guide people further in finding the complete set of tools needed to build an application.
add note re: handling events in capture phase
fix typo in addons.update() $splice command help
Merge pull request #2630 from shamrin/patch-1

fix typo in addons.update() $splice command help
Give context aware message if markup reuse fails

The context is an extra message with comparison of where server and
client markup started to differ.
Merge pull request #2629 from arnihermann/diff-msg-on-checksum-fail

Give context aware message if markup reuse fails
Fix addons documentation of development only part