We (the cujojs team) are getting way too many inquiries (aka "complaints"
:) ) about a similar situation.  When using plugins, there's no standard
way to propagate loading errors back to the AMD loader.  (Side note:
relying on time-outs in the loader to detect loading errors in plugins is
not a solution, imho.  It's impossible to determine the correct value.)

curl.js adds a `require.reject(ex)` callback to the `require` injected into
the plugin's load method.  curl.js listens to that function so it can
handle the error and pass it on to any handlers the dev has added.  We use
this in all our plugins to signal that the plugin-based resource (legacy
javascript, css file, etc.) didn't load.

The name "reject" is certainly open for debate -- as is the possibility of
changing the load method's signature instead.  Regardless, something like
this would seem to go well with the `require(deps, callback, errback)`
feature.

Thoughts?

-- John