pgsql: Clean up error cases in psql's COPY TO STDOUT/FROM STDIN code.

Clean up error cases in psql's COPY TO STDOUT/FROM STDIN code.

Adjust handleCopyOut() to stop trying to write data once it's failed
one time. For typical cases such as out-of-disk-space or broken-pipe,
additional attempts aren't going to do anything but waste time, and
in any case clean truncation of the output seems like a better behavior
than randomly dropping blocks in the middle.

Also remove dubious (and misleadingly documented) attempt to force our way
out of COPY_OUT state if libpq didn't do that. If we did have a situation
like that, it'd be a bug in libpq and would be better fixed there, IMO.
We can hope that commit fa4440f51628d692f077d54b8313aea31af087ea took care
of any such problems, anyway.

Also fix longstanding bug in handleCopyIn(): PQputCopyEnd() only supports
a non-null errormsg parameter in protocol version 3, and will actively
fail if one is passed in version 2. This would've made our attempts
to get out of COPY_IN state after a failure into infinite loops when
talking to pre-7.4 servers.

Back-patch the COPY_OUT state change business back to 9.2 where it was
introduced, and the other two fixes into all supported branches.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/b8f00a46bc4ae77c09f4564f3b3c675fb9e51974

Modified Files
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src/bin/psql/copy.c | 75 +++++++++++++++++++++++++--------------------------
1 file changed, 37 insertions(+), 38 deletions(-)