pgsql: More GIN refactoring.

More GIN refactoring.

Separate the insertion payload from the more static portions of GinBtree.
GinBtree now only contains information related to searching the tree, and
the information of what to insert is passed separately.

Add root block number to GinBtree, instead of passing it around all the
functions as argument.

Split off ginFinishSplit() from ginInsertValue(). ginFinishSplit is
responsible for finding the parent and inserting the downlink to it.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/ce5326eed386959aac7a322880896ddeade7fd52

Modified Files
--------------
src/backend/access/gin/ginbtree.c | 182 ++++++++++++++++++++-------------
src/backend/access/gin/gindatapage.c | 168 ++++++++++++++++--------------
src/backend/access/gin/ginentrypage.c | 96 +++++++++--------
src/backend/access/gin/ginget.c | 2 +-
src/backend/access/gin/gininsert.c | 11 +-
src/backend/access/gin/ginxlog.c | 22 ++--
src/include/access/gin_private.h | 46 ++++++---
7 files changed, 309 insertions(+), 218 deletions(-)