pgsql: include_if_exists facility for config file.

include_if_exists facility for config file.

This works the same as include, except that an error is not thrown
if the file is missing. Instead the fact that it's missing is
logged.

Greg Smith, reviewed by Euler Taveira de Oliveira.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6d09b2105fb5fa6e6245e7b024bfbe465b1041ee

Modified Files
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doc/src/sgml/config.sgml          |   12 ++++++++++
src/backend/utils/misc/guc-file.l |   41 +++++++++++++++++++++++++++++-------
src/include/utils/guc.h           |    2 +-
3 files changed, 46 insertions(+), 9 deletions(-)