Fix Issue 7036: java.math.BigInteger ctor accepts invalid input.

OpenSSL's BN library accepts pretty much all input, so if we want to follow
Java's rules, we have to implement them ourselves.

(The FormatterTest change is unrelated and fixes outstanding build breakage
caused by me.)

Bug: http://code.google.com/p/android/issues/detail?id=7036
Change-Id: I0f5413b56fad9289644927672bebf7c3d57e8042
4 files changed