Added validation for classes with private methods

[jmf-tls]

No description provided.

[jmf-tls]

With the new private method the tests in FakingEverythingTest fail with the following errors:

[INFO] Running mockit.FakingEverythingTest
[ERROR] Tests run: 4, Failures: 0, Errors: 4, Skipped: 0, Time elapsed: 0.105 s <<< FAILURE! - in mockit.FakingEverythingTest
[ERROR] publicAdviceMethodInPublicFakeClass(mockit.FakingEverythingTest)  Time elapsed: 0.078 s  <<< ERROR!
java.lang.IllegalArgumentException: Unsupported fake for private method TargetClass#doSomethingInternal()V found
	at mockit.FakingEverythingTest.publicAdviceMethodInPublicFakeClass(FakingEverythingTest.java:153)

[ERROR] fakeEveryMethodInSingleClassWithAdviceOnly(mockit.FakingEverythingTest)  Time elapsed: 0.005 s  <<< ERROR!
java.lang.IllegalArgumentException: Unsupported fake for private method TargetClass#doSomethingInternal()V found
	at mockit.FakingEverythingTest.fakeEveryMethodInSingleClassWithAdviceOnly(FakingEverythingTest.java:74)

[ERROR] fakeEveryMethodInSingleClass(mockit.FakingEverythingTest)  Time elapsed: 0.005 s  <<< ERROR!
java.lang.IllegalArgumentException: Unsupported fake for private method TargetClass#doSomethingInternal()V found
	at mockit.FakingEverythingTest.fakeEveryMethodInSingleClass(FakingEverythingTest.java:26)

[ERROR] fakeEveryMethodInClassHierarchy(mockit.FakingEverythingTest)  Time elapsed: 0.009 s  <<< ERROR!
java.lang.IllegalArgumentException: Unsupported fake for private method TargetClass#doSomethingInternal()V found
	at mockit.FakingEverythingTest.fakeEveryMethodInClassHierarchy(FakingEverythingTest.java:87)