Add is_posnumericint

to allow easy validation of positive integers.
It returns true for an actual (int) type with a value > 0 or a string that looks like an ordinary positive integer like "1" "345" "1000".
It returns false for:
a) (int) type 0 or negative
b) any (float) or (boolean) type
c) any ordinary string that is not a number "abc" "true" "false"...
d) other strings that might cast to an integer, but are not in "ordinary decimal" form - "2e3" "0xff"
e) strings that start with "0" and might look positive - "01" "00999" - such strings could be a nuisance if they were validated, stored in a config and passed to utilities in conf files or as command line parameters.