Refactor PQescape

[daurnimator]

PQescape has a single callsite (in conn_escape). IMO it could be improved upon (and possibly even removed entirely):

• Remove syslog calls (and hence dependency)
• Remove strlcpy calls (and hence dependency on libbsd on linux)
• Remove conn == NULL branch, as the callsite always provides a connection object
• Use lua memory management functions so we get correct error handling and cleanup
• No longer use a static buffer (char buf[1024];) in conn_escape

[daurnimator]

This was fixed in commit 92893375c629f0bf583510f6f5ff98a5193a97ed