Use strncasecmp instead of strncmp when comparing the password scheme.

Use strncasecmp instead of strncmp when comparing the password scheme.
This change could theoretically affect some people who actually have one
of the scheme's in lower case in their password, but this is extremely
unlikely in the real world.

Pointed out by David Diggles (david <at> elven <dot> com <dot> au)
OK sthen@