pgsql: Add support for piping COPY to/from an external program.

Add support for piping COPY to/from an external program.

This includes backend "COPY TO/FROM PROGRAM '...'" syntax, and corresponding
psql \copy syntax. Like with reading/writing files, the backend version is
superuser-only, and in the psql version, the program is run in the client.

In the passing, the psql \copy STDIN/STDOUT syntax is subtly changed: if you
the stdin/stdout is quoted, it's now interpreted as a filename. For example,
"\copy foo from 'stdin'" now reads from a file called 'stdin', not from
standard input. Before this, there was no way to specify a filename called
stdin, stdout, pstdin or pstdout.

This creates a new function in pgport, wait_result_to_str(), which can
be used to convert the exit status of a process, as returned by wait(3),
to a human-readable string.

Etsuro Fujita, reviewed by Amit Kapila.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/3d009e45bde2a2681826ef549637ada76508b597

Modified Files
--------------
contrib/file_fdw/file_fdw.c             |    4 +-
doc/src/sgml/keywords.sgml              |    7 +
doc/src/sgml/ref/copy.sgml              |   50 +++++++-
doc/src/sgml/ref/psql-ref.sgml          |   33 ++++--
src/backend/commands/copy.c             |  205 ++++++++++++++++++++++--------
src/backend/nodes/copyfuncs.c           |    1 +
src/backend/nodes/equalfuncs.c          |    1 +
src/backend/parser/gram.y               |   48 ++++++--
src/backend/storage/file/fd.c           |   98 ++++++++++++++-
src/bin/psql/copy.c                     |  131 ++++++++++++++++----
src/bin/psql/stringutils.c              |    5 +-
src/bin/psql/stringutils.h              |    2 +
src/include/commands/copy.h             |    2 +-
src/include/nodes/parsenodes.h          |    1 +
src/include/parser/kwlist.h             |    1 +
src/include/port.h                      |    3 +
src/include/storage/fd.h                |    4 +
src/interfaces/ecpg/preproc/ecpg.addons |    2 +-
src/port/Makefile                       |    3 +-
src/port/exec.c                         |   37 ++----
src/port/wait_error.c                   |   92 ++++++++++++++
21 files changed, 581 insertions(+), 149 deletions(-)