Update out of date comments in pg_trgm

Commit be8a7a6 changed the check_only parameter to a flag array
but missed updating all comments. Update, and fix a related typo.

Discussion: https://postgr.es/m/9732D8A2-EABD-4F5B-8BA0-A97DA4AB51A7@yesql.se

Author: danielgustafsson

contrib/pg_trgm/trgm_op.c

@@ -442,14 +442,15 @@ comp_ptrgm(const void *v1, const void *v2)
 
 /*
  * Iterative search function which calculates maximum similarity with word in
- * the string. But maximum similarity is calculated only if check_only == false.
+ * the string. Maximum similarity is only calculated only if the flag
+ * WORD_SIMILARITY_CHECK_ONLY isn't set.
  *
  * trg2indexes: array which stores indexes of the array "found".
  * found: array which stores true of false values.
  * ulen1: count of unique trigrams of array "trg1".
  * len2: length of array "trg2" and array "trg2indexes".
  * len: length of the array "found".
- * lags: set of boolean flags parameterizing similarity calculation.
+ * flags: set of boolean flags parameterizing similarity calculation.
  * bounds: whether each trigram is left/right bound of word.
  *
  * Returns word similarity.