pgsql: Implement streaming xlog for backup tools

Implement streaming xlog for backup tools

Add option for parallel streaming of the transaction log while a
base backup is running, to get the logfiles before the server has
removed them.

Also add a tool called pg_receivexlog, which streams the transaction
log into files, creating a log archive without having to wait for
segments to complete, thus decreasing the window of data loss without
having to waste space using archive_timeout. This works best in
combination with archive_command - suggested usage docs etc coming later.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d9bae5317300cf983dd9f01cc2e561c0eecd109a

Modified Files
--------------
doc/src/sgml/ref/allfiles.sgml         |    1 +
doc/src/sgml/ref/pg_basebackup.sgml    |   65 ++++-
doc/src/sgml/ref/pg_receivexlog.sgml   |  270 ++++++++++++++++
doc/src/sgml/reference.sgml            |    1 +
src/bin/pg_basebackup/.gitignore       |    1 +
src/bin/pg_basebackup/Makefile         |   15 +-
src/bin/pg_basebackup/pg_basebackup.c  |  538 +++++++++++++++++++++++---------
src/bin/pg_basebackup/pg_receivexlog.c |  465 +++++++++++++++++++++++++++
src/bin/pg_basebackup/receivelog.c     |  398 +++++++++++++++++++++++
src/bin/pg_basebackup/receivelog.h     |   22 ++
src/bin/pg_basebackup/streamutil.c     |  165 ++++++++++
src/bin/pg_basebackup/streamutil.h     |   22 ++
src/tools/msvc/Mkvcbuild.pm            |    7 +
13 files changed, 1805 insertions(+), 165 deletions(-)