Replace direct inclusions of c.h with inclusion of postgres.h,

contrib/fulltextindex/fti.c

src/backend/port/dynloader/aix.c

src/backend/port/dynloader/hpux.c

src/backend/port/dynloader/ultrix4.c

src/backend/storage/buffer/s_lock.c

src/backend/utils/error/format.c

src/backend/utils/mmgr/oset.c

src/backend/utils/mmgr/palloc.c

src/include/libpq/pqcomm.h

src/interfaces/libpq/pqsignal.h