pgsql: Kill pg_basebackup background process when exiting

Kill pg_basebackup background process when exiting

If an error occurs in the foreground (backup) process of pg_basebackup,
and we exit in a controlled way, the background process (streaming
xlog process) would stay around and keep streaming.

Branch
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REL9_3_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/c90204c605b7e12858e52b6af6efdbf3cb1c1bc4

Modified Files
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src/bin/pg_basebackup/pg_basebackup.c  |   21 +++++++++++++++++++++
src/bin/pg_basebackup/pg_receivexlog.c |    7 +++++++
src/bin/pg_basebackup/streamutil.h     |    6 ------
3 files changed, 28 insertions(+), 6 deletions(-)