pgsql: Recursively fsync() the data directory after a crash.

Recursively fsync() the data directory after a crash.

Otherwise, if there's another crash, some writes from after the first
crash might make it to disk while writes from before the crash fail
to make it to disk.  This could lead to data corruption.

Back-patch to all supported versions.

Abhijit Menon-Sen, reviewed by Andres Freund and slightly revised
by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/2ce439f3379aed857517c8ce207485655000fc8e

Modified Files
--------------
src/backend/access/transam/xlog.c |   42 ++++++++++++++
src/backend/storage/file/fd.c     |  115 +++++++++++++++++++++++++++++++++++++
src/include/storage/fd.h          |    2 +
3 files changed, 159 insertions(+)