cmp: add -n, --bytes to limit number of bytes to compare

[kevans]

Summary

This is compatible with GNU cmp.

Sponsored by: Klara, Inc.

[markj]

usr.bin/cmp/cmp.c

93

for consistency with handling of expand_number() errors elsewhere.

97

Cases are typically sorted, i.e., case 'n' should come after case 'l'.

usr.bin/cmp/link.c

77

We pass skip1 and skip2 as parameters to each comparison function, but limit a global var. Is there any reason it can't also be a function parameter?

[kevans]

usr.bin/cmp/cmp.c

97

I fixed the sorting in the other two, as well...

[kevans]

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