Make comment in fmgr.h match the one in fmgr.c.
Incompletely quoting an API spec does nobody any good.  Noted by
Paul Jungwirth.  Looks like the discrepancy was my fault originally :-(
Discussion:
@@ -489,7 +489,8 @@ extern int no_such_variable
/* These are for invocation of a specifically named function with a
* directly-computed parameter list. Note that neither arguments nor result
- * are allowed to be NULL.
+ * are allowed to be NULL. Also, the function cannot be one that needs to
+ * look at FmgrInfo, since there won't be any.
*/
extern Datum DirectFunctionCall1Coll(PGFunction func, Oid collation,
Datum arg1);
