[16/24] +-Infinity: correct assumptions

[16/24] +-Infinity: correct assumptions

    finite:         U -> F      (not sure about this, but NegativeInfinity already was =F)
    integer:        F -> U
    rational:       T -> U
    infinitesimal:  U -> F

Also Infinity and NegativeInfinity lacked assumptions tests, so I wrote them.

References
----------

http://en.wikipedia.org/wiki/Finite
http://en.wikipedia.org/wiki/Infinitesimal
http://en.wikipedia.org/wiki/Infinity

Signed-off-by: Kirill Smelkov <kirr@landau.phys.spbu.ru>
Signed-off-by: Ondrej Certik <ondrej@certik.cz>
Signed-off-by: Mateusz Paprocki <mattpap@gmail.com>