pgsql: Move copydir.c from src/port to src/backend/storage/file The

Log Message:
-----------
Move copydir.c from src/port to src/backend/storage/file

The previous commit to make copydir() interruptible prevented
postgres.exe from linking on MinGW and Cygwin, because on those
platforms libpgport_srv.a can't freely reference symbols defined
by the backend.  Since that code is already backend-specific anyway,
just move the whole file into the backend rather than adding further
kludges to deal with the symbols needed by CHECK_FOR_INTERRUPTS().

This probably needs some further cleanup, but this commit just moves
the file as-is, which should hopefully be enough to turn the
buildfarm green again.

Modified Files:
--------------
    pgsql/src/backend/storage/file:
        Makefile (r1.13 -> r1.14)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/file/Makefile?r1=1.13&r2=1.14)
    pgsql/src/port:
        Makefile (r1.38 -> r1.39)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/Makefile?r1=1.38&r2=1.39)

Added Files:
-----------
    pgsql/src/backend/storage/file:
        copydir.c (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/storage/file/copydir.c?rev=1.1&content-type=text/x-cvsweb-markup)

Removed Files:
-------------
    pgsql/src/port:
        copydir.c
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/port/copydir.c)