Capitalization fixes

doc/src/sgml/config.sgml

doc/src/sgml/libpq.sgml

doc/src/sgml/plpgsql.sgml

doc/src/sgml/spi.sgml

doc/src/sgml/storage.sgml

src/backend/bootstrap/bootparse.y

src/backend/port/ipc_test.c

src/backend/port/win32/signal.c

src/backend/storage/buffer/bufmgr.c

src/backend/storage/ipc/sinvaladt.c

src/backend/storage/lmgr/proc.c

src/backend/storage/smgr/smgrtype.c

src/backend/utils/cache/inval.c

src/backend/utils/cache/syscache.c

src/backend/utils/init/postinit.c

src/interfaces/ecpg/ecpglib/execute.c

src/test/examples/testlibpq2.c

src/test/regress/pg_regress.c