redact passwords in parse config errors

Redact passwords when printing the parseConfigError in a best effort manner.
This prevents people from leaking the password into logs, if they just print the error in logs.

export_test.go

@@ -0,0 +1,11 @@
+// File export_test exports some methods for better testing.
+
+package pgconn
+
+func NewParseConfigError(conn, msg string, err error) error {
+	return &parseConfigError{
+		connString: conn,
+		msg:        msg,
+		err:        err,
+	}
+}