RFR(L): 8197405: Improve messages of AbstractMethodErrors and IncompatibleClassChangeErrors.

[Lindenmaier, Goetz]

Hi, 

This change improves the messages of AbstractMethodErrors and IncompatibleClassChangeErrors.
Please review. 
http://cr.openjdk.java.net/~goetz/wr18/8197405-ameExMsg/webrev.01/

It adds tests that check some of the improved messages.
The tests check the following improvements:

AbstractMethodErrors:

test_ameInt, test case 1:
before: no message / null
after:  Missing implementation of interface method MyAbstractInt.anAbstractMethod()Ljava/lang/String;

test_ameInt, test case 2:
before: no message / null
after:  Class ImplementsSomeFunctionsInt does not implement the requested method
        aFunctionOfMyInterface()Ljava/lang/String; inherited from interface MyInterfaceInt1

test_ame, interpreted:
before: no message / null
after:  Missing implementation of interface method MyInterface.aFunctionOfMyInterface()V

test_ame, compiled:
before: MyAbstract.aFunctionOfMyInterface()V
after:  Class ImplementsSomeFunctions does not implement the requested method
        aFunctionOfMyInterface()V inherited from abstract class MyAbstract

IncompatibleClassChangeErrors:

test_icc_compiled_itable_stub
before: vtable stub
after:  Class ICC_B does not implement the requested interface ICC_iB

Best regards,
  Goetz.