Avoid prototype property name conflict in cache key

The value that is contained as key of `Object.prototype` couldn't be dasherize.

For examples:
``` javascript
Ember.String.dasherize('toString'); // function toString() { [native code] }
```

This reason is that cache is object (not Hash or Map) inherited
`Object.prototype` as its property.

`Object` should not be used as key of cache that accept any keys from user
input.
So I used prefix `:` as the key of cache.
Remove unnecessary '#'

'#' is unnecessary for putting return value.
Merge pull request #2207 from tricknotes/remove-unnecessary

Remove unnecessary '#'
Merge pull request #2204 from tricknotes/stop-using-cache-for-dasherize

Stop using cache for `Ember.String.dasherize`
I apparently give terrible advice. the prefix is needed turns out JS
can do this lookup for us.
Merge pull request #2208 from stefanpenner/master

I apparently am an idiot. Thanks @kselden for pointing this out.
We only need to see the versions logged once per session.
bump rake-pipeline
Merge pull request #2209 from stefanpenner/master

Some minor annoyances.
Normalized Ember.run.later and Ember.run.next behavior.

In particular, callbacks for both are now guaranteed to be run from
within a totally separate run loop; previously, though the docs
suggested so, there was no guarantee the code would be run from
within a run loop at all, much less a separate one.

Ember.run.next is now shorthand for Ember.run.later with
1ms wait, as a result, there was a chunk of `next` code
that could be removed/consolidated in to `later`.

Fixes #913
Merge pull request #2199 from machty/runloop-later

Normalized Ember.run.later and Ember.run.next behavior.
Update Gemfile.lock
Handle 'undefined' element properties - Fixes #2170
Update assert message for model hook in Ember.Route
Merge pull request #2216 from pangratz/update/assert_message

Update assert message for model hook in Ember.Route
Update ember-dev to fix tests
use charAt() instead of brackets to access string character
IE7 does not support bracket access to string characters and errors:
http://stackoverflow.com/questions/5943726/string-charatx-or-stringx
Merge pull request #2221 from craigteegarden/ie7-bracket-to-charAt

use charAt() instead of brackets to access string character
Added documentation to the append method

I know it's stated on the `rootElement` but I feel re-iterating it here is also helpful.

Fixed typo
Merge pull request #2222 from lsdafjklsd/patch-1

Added documentation to the append method