Add a constant function to the float module that returns positive infinity.
This is implemented for the C, Java, and C# backends.
The Erlang backend currently does not support it
library/float.m:
Add the new function.
Address review comments from Paul about my previous change.
tests/hard_coded/Mmakefile:
tests/hard_coded/test_infinity.{m,exp}:
Test various operations involving infinity.
NEWS:
Announce the addition.
