pgsql: Inherit max_safe_fds to child processes in EXEC_BACKEND mode.

Inherit max_safe_fds to child processes in EXEC_BACKEND mode.

Postmaster sets max_safe_fds by testing how many open file descriptors it
can open, and that is normally inherited by all child processes at fork().
Not so on EXEC_BACKEND, ie. Windows, however. Because of that, we
effectively ignored max_files_per_process on Windows, and always assumed
a conservative default of 32 simultaneous open files. That could have an
impact on performance, if you need to access a lot of different files
in a query. After this patch, the value is passed to child processes by
save/restore_backend_variables() among many other global variables.

It has been like this forever, but given the lack of complaints about it,
I'm not backpatching this.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/5762a4d9098ac0cba789ddd26286ac85c2d316f2

Modified Files
--------------
src/backend/postmaster/postmaster.c |    3 +++
src/backend/storage/file/fd.c       |    2 +-
src/include/storage/fd.h            |    5 +++++
3 files changed, 9 insertions(+), 1 deletions(-)