Assertion if incrementProperty given non-numeric value

Includes fixes for incrementProperty and decrementProperty.

Ember.assert in incrementProperty and decrementProperty discourages any attempt to increment/decrement by a non-numeric value or Infinity.

Retains support for 0 increment

Added tests for NaN, non-numeric string, and Infinity
Aborts/redirects in willTransition don't enter LoadingRoute

Closes #3034. Closes #2987.
Merge pull request #3040 from realityendshere/increment-property-nan

Fix incrementProperty/decrementProperty to handle NaN
linkTo param of 0 should be treated as a url param

Part of this fix is in router.js, the other part in Ember.

`linkTo` was generating incorrect hrefs when the provided
parameter was the number 0 (even though '0') worked. Now it
will work as expected without requiring casting to a string
first.

Also removed some unnecessary code on Ember's side to check that all
bound params are truthy before reporting that `routeArgs` changed in
`LinkView`.
Clarified Ember.warn message for linkTo loading state