Changed InternalGetCharCount to iterate the bytes as InternalGetChars.
Added class EncodingTester that can be used to test fallbacks.
EncodingTester is a testing helper class with a method TestDecoderFallback that makes DecoderFalback testing  easier.
Added UTF8EncodingTest.EncodingFallback.
EncodingFallback tests for multiple invalid inputs the unknownBytes that are given to the DecoderFallback.
Changed UTF8Encoding to call fallback with whole byte sequences.
Removed unnecessary parameters ref byte [] bufferArg.
This changes are required by UTF8EncodingTest.EncodingFallback that in some cases is expecting multibyte values..
Changed overlong byte to be processed again.
The byte is processed again because it can be the begin of a new multi-byte encoded character.
Merge pull request #1251 from esdrubal/utf8encoding

UTF8Encoding Fallback