Merge pull request #7 from joshuastray/plugin_fb

feature #5592: fix facebook plugin
Feature #5592: Fix Pluginx callback functions JSB context issue
Feature #5592: Fix callback issue for "dialog" alias function
Feature #5592: Improve message for callbacks
Feature #5592: Add direct callback to ProtocolShare
Merge branch 'plugin_fb' of https://github.com/pandamicro/plugin-x into plugin_fb
Feature #5592: Fix compilation issue in ProtocolShare
Merge branch 'plugin_fb' of https://github.com/pandamicro/plugin-x into plugin_fb
add std::function callback