RFR [9]: 8181295: Document that SecurityManager::checkPackageAccess may be called by the VM

[Sean Mullan]

Please review this clarification to the 
SecurityManager::checkPackageAccess method to note that the method may 
be called by the Virtual Machine when loading classes:

http://cr.openjdk.java.net/~mullan/webrevs/8181295/webrev.00/
A small correction was also made to the checkPackageDefinition method to 
note that it may be called by the defineClass (and not the loadClass) 
method of class loaders.

--Sean