pgsql: Avoid integer overflow in hstore_to_json().

Avoid integer overflow in hstore_to_json().

The length of the output buffer was calculated based on the size of the
argument hstore. On a sizeof(int) == 4 platform and a huge argument, it
could overflow, causing a too small buffer to be allocated.

Refactor the function to use a StringInfo instead of pre-allocating the
buffer. Makes it shorter and more readable, too.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/0c5783ff301ae3e470000c918bfc2395129de4c5

Modified Files
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contrib/hstore/hstore_io.c |  150 ++++++++++++--------------------------------
1 file changed, 41 insertions(+), 109 deletions(-)