can.compute evaluations for the default Mustache handlers
Added compute check for context objects when resolving object references in mustache.
Tests for compute checks for the various default helpers
Fixing can.ajax for Mootools

- onError is only for JSON parsing errors, Ajax communication errors are
in onFailure
- do not clobber mootools native onSuccess and onFailure if passed in
- remove local JSON parsin and use Mootools for it
Merge pull request #303 from scorphus/master

Treat "--" as delimiter of empty element
Merge pull request #300 from tracer99/master

Fixing can.ajax with mootools
Merge pull request #292 from bmomberger-reciprocity/computes_for_default_helpers

can.compute evaluations for the default Mustache handlers