Use `to_buf` for composite escaping.
Use `to_buf` for composite escaping.

Replace the `into_buf` (using the tail of the output buffer as an
intermediate buffer) with a `to_buf`.  It may be slightly faster in some
cases.

jtv/libpqxx,jtv/libpqxx,jtv/libpqxx,jtv/libpqxx