pgsql: Cosmetic improvements to group locking.

Cosmetic improvements to group locking.

Reflow text in lock manager README so that it fits within 80 columns.
Correct some mistakes.  Expand the README to explain not only why group
locking exists but also the data structures that support it.  Improve
comments related to group locking several files.  Change the name of a
macro argument for improved clarity.

Most of these problems were reported by Tom Lane, but I found a few
of them myself.

Robert Haas and Tom Lane

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/d91a4a6c85d360678310470854d5d932d1833aa8

Modified Files
--------------
src/backend/storage/lmgr/README     | 104 +++++++++++++++++++++++-------------
src/backend/storage/lmgr/deadlock.c |  21 +++++---
src/backend/storage/lmgr/proc.c     |  15 ++++--
src/include/storage/lock.h          |   7 +--
src/include/storage/proc.h          |   8 +--
5 files changed, 102 insertions(+), 53 deletions(-)