size_t vs "unsigned long"

Traditionally, inside git, we have used the length of things with "unsigned long" for pretty much anything, except where we wanted the length exactly sized we used int32_t, uint64_t and friends.

A few places pass pointer to unsigned long as the second parameter to strbuf_detach(), triggering type mismatch warnings. An easy way out is to change strbuf_detach() to take a pointer to ulong but I think it is going backwards. Most places that use "unsigned long" can safely be converted (and made more correct) to use size_t.

Any opinions?