pgsql: Add contrib/file_fdw foreign-data wrapper for reading files via

Add contrib/file_fdw foreign-data wrapper for reading files via COPY.

This is both very useful in its own right, and an important test case
for the core FDW support.

This commit includes a small refactoring of copy.c to expose its option
checking code as a separately callable function. The original patch
submission duplicated hundreds of lines of that code, which seemed pretty
unmaintainable.

Shigeru Hanada, reviewed by Itagaki Takahiro and Tom Lane

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/7c5d0ae7078456bfeedb2103c45b9a32285c2631

Modified Files
--------------
contrib/Makefile | 1 +
contrib/README | 4 +
contrib/file_fdw/.gitignore | 2 +
contrib/file_fdw/Makefile | 21 ++
contrib/file_fdw/data/agg.bad | 4 +
contrib/file_fdw/data/agg.csv | 4 +
contrib/file_fdw/data/agg.data | 4 +
contrib/file_fdw/expected/.gitignore | 1 +
contrib/file_fdw/file_fdw--1.0.sql | 15 +
contrib/file_fdw/file_fdw.c | 536 +++++++++++++++++++++++++++++++
contrib/file_fdw/file_fdw.control | 5 +
contrib/file_fdw/input/file_fdw.source | 131 ++++++++
contrib/file_fdw/output/file_fdw.source | 225 +++++++++++++
contrib/file_fdw/sql/.gitignore | 1 +
doc/src/sgml/contrib.sgml | 1 +
doc/src/sgml/file-fdw.sgml | 127 ++++++++
doc/src/sgml/filelist.sgml | 1 +
src/backend/commands/copy.c | 138 +++++---
src/include/commands/copy.h | 5 +-
19 files changed, 1171 insertions(+), 55 deletions(-)