Warns if plugin class not instantiable

The class returned from NSClassFromString is checked and a warning is produced if it is nil.
Merge pull request #15 from NatWeiss/patch-1

Warns if plugin class not instantiable
add 64bit
fix redefine bugs
IOSIAP didn't fish remove it
Merge pull request #38 from wuzhiming/PluginXJSB

add 64bit support