pgsql-server: vacuum.c refactoring .

Log Message:
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vacuum.c refactoring

. rename variables
. cur_buffer -> dst_buffer
. ToPage -> dst_page
. cur_page -> dst_vacpage
. move variable declarations into block where variable is used
. various Asserts instead of elog(ERROR, ...)
. extract functionality from repair_frag() into new routines
. move_chain_tuple()
. move_plain_tuple()
. update_hint_bits()
. create type ExecContext
. add comments

Manfred Koizar

Modified Files:
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pgsql-server/src/backend/commands:
vacuum.c (r1.280 -> r1.281)
(http://developer.postgresql.org/cvsweb.cgi/pgsql-server/src/backend/commands/vacuum.c.diff?r1=1.280&r2=1.281)