Fix thinko: have trueTriConsistentFn return GIN_TRUE.

While we're at it, also improve comments in ginlogic.c.

src/backend/access/gin/ginlogic.c

@@ -3,18 +3,25 @@
  * ginlogic.c
  *	  routines for performing binary- and ternary-logic consistent checks.
  *
- * A GIN operator class provides a consistent function which checks if a
- * tuple matches a qual, when the given set of keys are present in the tuple.
- * The consistent function is passed a TRUE/FALSE argument for every key,
- * indicating if that key is present, and it returns TRUE or FALSE. However,
- * a GIN scan can apply various optimizations, if it can determine that an
- * item matches or doesn't match, even if it doesn't know if some of the keys
- * are present or not. Hence, it's useful to have a ternary-logic consistent
- * function, where each key can be TRUE (present), FALSE (not present),
- * or MAYBE (don't know if present). This file provides such a ternary-logic
- * consistent function,  implemented by calling the regular boolean consistent
- * function many times, with all the MAYBE arguments set to all combinations
- * of TRUE and FALSE.
+ * A GIN operator class can provide a boolean or ternary consistent
+ * function, or both.  This file provides both boolean and ternary
+ * interfaces to the rest of the GIN code, even if only one of them is
+ * implemented by the opclass.
+ *
+ * Providing a boolean interface when the opclass implements only the
+ * ternary function is straightforward - just call the ternary function
+ * with the check-array as is, and map the GIN_TRUE, GIN_FALSE, GIN_MAYBE
+ * return codes to TRUE, FALSE and TRUE+recheck, respectively.  Providing
+ * a ternary interface when the opclass only implements a boolean function
+ * is implemented by calling the boolean function many times, with all the
+ * MAYBE arguments set to all combinations of TRUE and FALSE (up to a
+ * certain number of MAYBE arguments).
+ *
+ * (A boolean function is enough to determine if an item matches, but a
+ * GIN scan can apply various optimizations if it can determine that an
+ * item matches or doesn't match, even if it doesn't know if some of the
+ * keys are present or not.  That's what the ternary consistent function
+ * is used for.)
  *
  *
  * Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
@@ -43,7 +50,7 @@
 #define	MAX_MAYBE_ENTRIES	4
 
 /*
- * A dummy consistent function for an EVERYTHING key. Just claim it matches.
+ * Dummy consistent functions for an EVERYTHING key.  Just claim it matches.
  */
 static bool
 trueConsistentFn(GinScanKey key)
@@ -54,7 +61,7 @@ trueConsistentFn(GinScanKey key)
 static GinLogicValue
 trueTriConsistentFn(GinScanKey key)
 {
-	return GIN_MAYBE;
+	return GIN_TRUE;
 }
 
 /*