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 #35 from joshuastray/develop

Feature #5027：add Android.mk for jsbindings
Solve the error config for eclipse in plugin uc.
Merge pull request #37 from natural-law/develop

Solve the error config for eclipse in plugin uc.
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
Feature #5363 add iOS iap into plugging
Feature #5363 add iOS iap into pluginX
Feature #5363 aFeature #5363 add iOS iap into pluginX
Feature #5363 aFeature #5363  remove test files
Safeguard for plugin object

On iOS and Android, without the safeguard, these runtime errors can occur:

    JS: assets/jsb/jsb_pluginx.js:1:ReferenceError: plugin is not defined
    JS: assets/jsb/jsb_pluginx.js:11:TypeError: plugin.ProtocolAds is undefined

This safeguard fixes the errors.
Feature #5363 aFeature #5363 add iOS iap into pluginX
Feature #5363 aFeature #5363 add iOS iap into pluginX
Feature #5363 aFeature #5363 add iOS iap into pluginX
·Feature #5363 aFeature #5363 add iOS iap into pluginX
Merge pull request #40 from wuzhiming/IOSIAP

Finish IOSIAP feature
Merge pull request #42 from NatWeiss/patch-4

Safeguard for plugin object