use check_in_args for xout validation to take advantage of polymorphic checks and allow constants for output [fixes #579]
use check_in_args for xout validation to take advantage of polymorphic checks and allow constants for output [fixes #579]

nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound,nikhilsinghmus/csound