Fixed a possible crash in gregorian::special_value_from_string if the string did not represent a valid special value. The find_match function now accepts the size of lookup tables rater than the maximum index.

[SVN r49875]

libs/date_time

@@ -1 +1 @@
-Subproject commit 4ea026b8356d6a62ba932ef880bd180b0e46d104
+Subproject commit 462d59604b66169c6532aa4d097736813d5a10e7