Improve to_str & from_str with better radix handling of integer types

[kvark]

"float::to_str()" does not have a radix parameter, working under base 10. We should preserve this behavior for integer types as well. We also need "to_str_radix()" and "from_str_radix()" functions for integer types.

[therealgymmy]

Agreed, the second parameter to float::to_str() specifies the number of significant digits, which is not consistent with integer types. (Before looking at float.rs, I thought it would take in a parameter specifying base just as in integer types and was quite puzzled by the result I got...)

to_str_radix can be added for now just by adding an additional trait for int. Although I don't think making another trait just to enable this feature is a good idea, it's probably the quickest fix.
You can just add the following code to either the rust lib code, or in one of your own files.

trait ToStrRadix { pure fn to_str_radix (radix: uint) -> str; }
impl int: ToStrRadix {
    pure fn to_str_radix (radix: uint) -> str { int::to_str(self, radix) }
}
// do the same for other types that support radix

[Kimundi]

Just a heads-up that I'm working on a unified interface for uint, int and float for that stuff right now.

[Kimundi]

This can be closed now, I think.