Tab completion for DROP CONSTRAINT

diff --git a/src/bin/psql/tab-complete.c b/src/bin/psql/tab-complete.c
new file mode 100644
index a1bb230..d55d8a0
*** a/src/bin/psql/tab-complete.c
--- b/src/bin/psql/tab-complete.c
*************** static const SchemaQuery Query_for_list_
*** 580,585 ****
--- 580,593 ----
  "       and pg_catalog.pg_table_is_visible(c2.oid)"
  
  /* the silly-looking length condition is just to eat up the current word */
+ #define Query_for_constraint_of_table \
+ "SELECT pg_catalog.quote_ident(conname) "\
+ "  FROM pg_catalog.pg_class c1, pg_catalog.pg_constraint con "\
+ " WHERE c1.oid=conrelid and (%d = pg_catalog.length('%s'))"\
+ "       and pg_catalog.quote_ident(c1.relname)='%s'"\
+ "       and pg_catalog.pg_table_is_visible(c1.oid)"
+ 
+ /* the silly-looking length condition is just to eat up the current word */
  #define Query_for_list_of_tables_for_trigger \
  "SELECT pg_catalog.quote_ident(relname) "\
  "  FROM pg_catalog.pg_class"\
*************** psql_completion(char *text, int start, i
*** 1337,1342 ****
--- 1345,1358 ----
  			 pg_strcasecmp(prev2_wd, "DROP") == 0 &&
  			 pg_strcasecmp(prev_wd, "COLUMN") == 0)
  		COMPLETE_WITH_ATTR(prev3_wd, "");
+ 	/* If we have TABLE <sth> DROP CONSTRAINT, provide list of constraints */
+ 	else if (pg_strcasecmp(prev4_wd, "TABLE") == 0 &&
+ 			 pg_strcasecmp(prev2_wd, "DROP") == 0 &&
+ 			 pg_strcasecmp(prev_wd, "CONSTRAINT") == 0)
+ 	{
+ 		completion_info_charp = prev3_wd;
+ 		COMPLETE_WITH_QUERY(Query_for_constraint_of_table);
+ 	}
  	/* ALTER TABLE ALTER [COLUMN] <foo> */
  	else if ((pg_strcasecmp(prev3_wd, "ALTER") == 0 &&
  			  pg_strcasecmp(prev2_wd, "COLUMN") == 0) ||