pgsql: Change ginMergeItemPointers to return a palloc'd array.

Change ginMergeItemPointers to return a palloc'd array.

That seems nicer than making it the caller's responsibility to pass a
suitable-sized array. All the callers were just palloc'ing an array anyway.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/bb42e21be274a71f6868ce2fc8fae2c15c3ecf66

Modified Files
--------------
src/backend/access/gin/gindatapage.c    |    7 +++---
src/backend/access/gin/gininsert.c      |    9 +++----
src/backend/access/gin/ginpostinglist.c |   40 ++++++++++++++++---------------
src/include/access/gin_private.h        |    6 ++---
4 files changed, 30 insertions(+), 32 deletions(-)