pgsql: Back-patch some minor bug fixes in GUC code.

Back-patch some minor bug fixes in GUC code.

In 9.4, fix a 9.4.1 regression that allowed multiple entries for a
PGC_POSTMASTER variable to cause bogus complaints in the postmaster log.
(The issue here was that commit bf007a27acd7b2fb unintentionally reverted
3e3f65973a3c94a6, which suppressed any duplicate entries within
ParseConfigFp. Back-patch the reimplementation just made in HEAD, which
makes use of an "ignore" field to prevent application of superseded items.)

Add missed failure check in AlterSystemSetConfigFile(). We don't really
expect ParseConfigFp() to fail, but that's not an excuse for not checking.

In both 9.3 and 9.4, remove mistaken assignment to ConfigFileLineno that
caused line counting after an include_dir directive to be completely wrong.

Branch
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REL9_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1afc1fe9c7bb72652ff9681c2e59a5751a33cda1

Modified Files
--------------
src/backend/utils/misc/guc-file.l | 50 ++++++++++++++++++++++++++++++-------
src/backend/utils/misc/guc.c | 6 ++++-
src/include/utils/guc.h | 6 ++++-
3 files changed, 51 insertions(+), 11 deletions(-)