Document r265555, addition of mrsas(4).

Sponsored by:	The FreeBSD Foundation
Handle ELF files with 65280 or more sections

If e_shnum or e_shstrndx are at least SHN_LORESERVE (0xff00) then an
escape value is used to indicate that the actual value is found in one
of section 0's fields.

Sponsored by:	DARPA, AFRL