Guard {Fixnum|Float}#frozen? from segfault and to be compatible with Ruby 1.9.3 behaviors

[kachick]

ref: https://github.com/topazproject/topaz/pull/845

$ PYTHONPATH=../pypy python ./bin/topaz_untranslated.py -e 'f = 0.1; p f.frozen?; f.freeze; p f.frozen?'
false
true

$ PYTHONPATH=../pypy python ./bin/topaz_untranslated.py -e 'f 1; p f.frozen?; f.freeze; p f.frozen?'
false
true

@alex How about like this?

[kachick]

Oops. This is My fault! I'll fix this.

PYTHONPATH=../pypy python ./bin/topaz_untranslated.py -e 'f = 1; p f.frozen?; f.freeze; p f.frozen?; p   2.frozen?'
false
true
true

[alex]

@kachick LGTM, before I merge, what's the plan for tests?

[kachick]

@alex Thanks for your review! I have added tests.