pgsql: Allow forcing nullness of columns during bootstrap.

Allow forcing nullness of columns during bootstrap.

Bootstrap determines whether a column is null based on simple builtin
rules. Those work surprisingly well, but nonetheless a few existing
columns aren't set correctly. Additionally there is at least one patch
sent to hackers where forcing the nullness of a column would be helpful.

The boostrap format has gained FORCE [NOT] NULL for this, which will be
emitted by genbki.pl when BKI_FORCE_(NOT_)?NULL is specified for a
column in a catalog header.

This patch doesn't change the marking of any existing columns.

Discussion: 20150215170014.GE15326@awork2.anarazel.de

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/eb68379c38202180bc8e33fb9987284e314b7fc8

Modified Files
--------------
doc/src/sgml/bki.sgml               |    9 +++--
src/backend/bootstrap/bootparse.y   |   13 +++++--
src/backend/bootstrap/bootscanner.l |    3 ++
src/backend/bootstrap/bootstrap.c   |   56 +++++++++++++++++++-----------
src/backend/catalog/Catalog.pm      |   24 +++++++++++--
src/backend/catalog/genbki.pl       |   65 +++++++++++++++++++++++++----------
src/backend/utils/Gen_fmgrtab.pl    |    2 +-
src/include/bootstrap/bootstrap.h   |    6 +++-
src/include/catalog/genbki.h        |    2 ++
9 files changed, 131 insertions(+), 49 deletions(-)