Replace deprecated chrome.extension use with chrome.runtime equivalents

chrome.extension.onMessage and chrome.extension.sendMessage are not
available in content scripts on Chromium 29.0.1547.65 (shipping in
Ubuntu 13.10).

This requires Chrome >= 26 for the newer chrome.runtime namespace.
Replace chrome.extension.onMessage with chrome.runtime for Opera
Merge pull request #586 from chizu/master

Replace deprecated chrome.extension use with chrome.runtime equivalents (fix for Chromium on Ubuntu 13.10)