Thread: pgsql: Cleanup for pglz_compress code: remove dead code, const-ify API

Log Message:
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Cleanup for pglz_compress code: remove dead code, const-ify API of
remaining functions, simplify pglz_compress's API to not require a useless
data copy when compression fails.  Also add a check in pglz_decompress that
the expected amount of data was decompressed.

Modified Files:
--------------
    pgsql/src/backend/access/heap:
        tuptoaster.c (r1.65 -> r1.66)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/access/heap/tuptoaster.c.diff?r1=1.65&r2=1.66)
    pgsql/src/backend/utils/adt:
        pg_lzcompress.c (r1.22 -> r1.23)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/pg_lzcompress.c.diff?r1=1.22&r2=1.23)
    pgsql/src/include/utils:
        pg_lzcompress.h (r1.12 -> r1.13)
        (http://developer.postgresql.org/cvsweb.cgi/pgsql/src/include/utils/pg_lzcompress.h.diff?r1=1.12&r2=1.13)