Updated the PR according to review comments.

PyNumber_ToBase() now raises SystemError for unsupported base instead of crashing. unicode_eq() asserts that unicode strings are ready (it is only called for hashed strings and if we have a hash they should be ready). PyCode_Optimize() returns the malformed bytecode unmodified. Other potentially non-unreachable code call now Py_FatalError(). Feel free to propose better messages. All other cases look truly unreachable to me.

Added support for the Intel and Microsoft compilers.