Add Win32 path handling for / vs. \ and drive letters.

src/Makefile.global.in

src/backend/commands/copy.c

src/backend/commands/dbcommands.c

src/backend/storage/file/fd.c

src/backend/utils/fmgr/dfmgr.c

src/backend/utils/init/findbe.c

src/backend/utils/init/miscinit.c

src/backend/utils/misc/database.c

src/bin/pg_controldata/pg_controldata.c

src/bin/pg_dump/pg_dump.c

src/bin/pg_dump/pg_dumpall.c

src/bin/pg_dump/pg_restore.c

src/bin/pg_resetxlog/pg_resetxlog.c

src/bin/psql/prompt.c

src/bin/psql/startup.c

src/bin/scripts/common.c

src/bin/scripts/common.h

src/include/c.h

src/interfaces/ecpg/ecpglib/connect.c

src/interfaces/ecpg/preproc/ecpg.c