track number of resources left to load, fixing race condition
add OS X support
Merge branch 'heisenbug' of https://github.com/peyton/WebViewJavascriptBridge

Conflicts:
	WebViewJavascriptBridge_OSX/WebViewJavascriptBridge_OSX.m
	WebViewJavascriptBridge_iOS/WebViewJavascriptBridge_iOS.m