pgsql: Refactor inCommit flag into generic delayChkpt flag.

Refactor inCommit flag into generic delayChkpt flag.
Rename PGXACT->inCommit flag into delayChkpt flag,
and generalise comments to allow use in other situations,
such as the forthcoming potential use in checksum patch.
Replace wait loop to look for VXIDs with delayChkpt set.
No user visible changes, not behaviour changes at present.

Simon Riggs, reviewed and rebased by Jeff Davis

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f21bb9cfb5646e1793dcc9c0ea697bab99afa523

Modified Files
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src/backend/access/transam/twophase.c | 16 +++---
src/backend/access/transam/xact.c | 8 +-
src/backend/access/transam/xlog.c | 28 ++++++---
src/backend/storage/ipc/procarray.c | 99 +++++++++++++++++---------------
src/backend/storage/lmgr/proc.c | 4 +-
src/include/storage/proc.h | 3 +-
src/include/storage/procarray.h | 4 +-
7 files changed, 89 insertions(+), 73 deletions(-)