* command.c, main.c (various places): Use ctype.h macros

	* command.c, main.c (various places):  Use ctype.h macros
	(such as isupper(x)),  instead of hard-wiring in ASCII-isms
	(such as (x >= 'A' && x <= 'Z')).
	(There are still more of these in other files.)
	* main.c (defined_command):  Lower-case the user's
	new command before entering it.  Needed because
	command lookup is case-insensitive (and also lower-cases).
	(Based on Metin's earlier patch.)