No connection timeout makes transaction timeout unreliable

A PostgreSQL connection attempt can hang indefinitely. This is often undesirable, eg. when you are using a TimeoutTracer to guarantee that transactions complete within a fixed time, or if you just don't want a script to be able to hang indefinitely because a connection pool is full.

PostgreSQL 7.4+ supports a 'connect_timeout' option in the libpq connection string. We need a way for this to be set. It may make sense to have this setting changed automatically from the PostgreSQLTimeoutTracer.