template function to check if a string is convertable to a specific numerical type

[Peter]

Currently, there are function is_int, is_double and is_float. It would be convenient to have a wrapper to these functions that will work in a template context.

It should behave very much like utility::convert with but rather than throwing when conversion is not possible, the function should return false. If conversion is possible obviously true should be returned.

For completeness, I think the functions should be overloaded/specialized for each numerical type.

If we wanna keep old is_* functions, I think we should reimplement them using this function.

[Peter]

fixed in [1312]