SSH2: Disallow the none MAC.
Merge pull request #425 from bantu/ssh-remove-none-mac

SSH2: Disallow the none MAC.

* bantu/ssh-remove-none-mac:
  SSH2: Disallow the none MAC.
Use toBits() as there is no bits property.
Add some test cases for SHA512.
Merge pull request #431 from bantu/issue/430

Fix "Undefined property: Math_BigInteger::$bits" + SHA512 tests.

* bantu/issue/430:
  Add some test cases for SHA512.
  Use toBits() as there is no bits property.