pgsql: Fix possible buffer overrun in contrib/pg_trgm.

Fix possible buffer overrun in contrib/pg_trgm.

Allow for the possibility that folding a string to lower case makes it
longer (due to replacing a character with a longer multibyte character).
This doesn't change the number of trigrams that will be extracted, but
it does affect the required size of an intermediate buffer in
generate_trgm(). Per bug #8821 from Ufuk Kayserilioglu.

Also install some checks that the input string length is not so large
as to cause overflow in the calculations of palloc request sizes.

Back-patch to all supported versions.

Branch
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REL8_4_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/72cce2c7806dbe872176d5af929b7f280f144d48

Modified Files
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contrib/pg_trgm/trgm_op.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)