Merge branch 'rj/header-check'

Header files clean-up. * rj/header-check: delta-islands.h: add missing forward declarations (hdr-check) midx.h: add missing forward declarations (hdr-check) refs/refs-internal.h: add missing declarations (hdr-check) refs/packed-backend.h: add missing declaration (hdr-check) refs/ref-cache.h: add missing declarations (hdr-check) ewah/ewok_rlw.h: add missing include (hdr-check) json-writer.h: add missing include (hdr-check) Makefile: add a hdr-check target