pgsql: In GIN recompression code, use mmemove rather than memcpy, for v

In GIN recompression code, use mmemove rather than memcpy, for vacuum.

When vacuuming a data leaf page, any compressed posting lists that are not
modified, are copied back to the buffer from a later location in the same
buffer rather than from  a palloc'd copy. IOW, they are just moved
downwards in the same buffer. Because the source and destination addresses
can overlap, we must use memmove rather than memcpy.

Report and fix by Alexander Korotkov.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/398cf255ad50db86ca665b75582317d4e795242a

Modified Files
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src/backend/access/gin/gindatapage.c |   15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)