[PATCH] arch/i386: Replace custom macro with isdigit()

Replace the custom is_digit() macro with isdigit() from <linux/ctype.h>

Signed-off-by: Tobias Klauser <tklauser@nuerscht.ch>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>