Protect against overly long savepoint names

Protect against overly long savepoint names

Per http://postgresql.org/docs/9.1/static/sql-syntax-lexical.html#SQL-SYNTAX-IDENTIFIERS,
the maximum identifier length works out to being 63 bytes (+1 for the
null terminator), so to avoid potential memory pressure by a 10GB string
somehow being passed in as the savepoint name, malloc no more than 64
bytes and copy no more than 63 bytes from the incoming name to the
escaped name.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>