Make a distinction between (1) WHERE clause constraints, (2) ON/USING

constraints on outer joins, and (3) ON/USING clause constraints on inner
joins.  Formerly, there was no distinctionb between 1 and 3, but RIGHT JOIN
needs to know the difference.  Make RIGHT JOIN aware of this difference and
add test cases.

FossilOrigin-Name: 0f6f61c3664cc87209c2a6f9b6df3a750d1510723fcde209c33db8feaf48bcf3

test/join7.test

@@ -175,5 +175,16 @@ foreach {id schema} {
     1    3    NULL NULL
     1    4    NULL NULL
   }
+  do_execsql_test join7-$id.12 {
+    SELECT a, b, c, d
+      FROM t2 FULL OUTER JOIN t1 ON b=c AND d<=0 ORDER BY +b, +d;
+  } {
+    NULL NULL 3    33
+    NULL NULL 4    44
+    NULL NULL 5    55
+    1    2    NULL NULL
+    1    3    NULL NULL
+    1    4    NULL NULL
+  }
 }  
 finish_test