Fixes for underscore.d.ts

* the type of elements in the array returned by pluck have no correlation to the type of elements in the source array - they actually relate to the values of the provided property name
* bind wasn't working for a function typed as "Function".  In our use case, we call _.throttle() then use the result in _.bind().
* the hash function passed into memoize may take multiple arguments
Add onMessageExternal to chrome.runtime
Merge pull request #1145 from rsmithh/patch-4

Add onMessageExternal to chrome.runtime
Merge pull request #1124 from derekcicerone/patch-17

Fixes for underscore.d.ts