Sort out paired double quotes in \connect, \password and \crosstabview.

In arguments, these meta-commands wrongly treated each pair as closing
the double quoted string.  Make the behavior match the documentation.
This is a compatibility break, but I more expect to find software with
untested reliance on the documented behavior than software reliant on
today's behavior.  Back-patch to 9.1 (all supported versions).

Reviewed by Tom Lane and Peter Eisentraut.

Security: CVE-2016-5424

src/bin/psql/psqlscan.l

@@ -1616,7 +1616,8 @@ psql_scan_slash_option(PsqlScanState state,
 							/* Keep the first quote, remove the second */
 							cp++;
 						}
-						inquotes = !inquotes;
+						else
+							inquotes = !inquotes;
 						/* Collapse out quote at *cp */
 						memmove(cp, cp + 1, strlen(cp));
 						mybuf.len--;