status.i4.v = is_valid_user(username.i1a.r [,bool nonuser_valid])

	This routine determines whether or not a string is a valid user
	name, i.e., whether or not the name is present and active in
	appdb.dbo.console_user.  This routine considers nonusers valid
	if and only if nonuser_valid has a value of true.

	username	ASCII username to test (USER_NAME_LEN characters)
	nonuser_valid	whether or not to consider nonusers as valid users
			(default is false)

	This function returns status values as follows:

	SQL_xxx			error accessing user name database
	TRUE			string is valid user name
	FALSE			string is not valid user name

	This function requires the following include files:

	cnsparam_h, clib_h, acnet_errors_h

	Related functions:

	is_valid_username, console_user_name_to_full_name, user_validation_c,