InnoDB: Fix compile warning.

innobase/include/trx0trx.h:
  Change trx_set_detailed_error's second argument to const char*.
innobase/trx/trx0trx.c:
  Change trx_set_detailed_error's second argument to const char*.

innobase/include/trx0trx.h

@@ -62,7 +62,7 @@ void
 trx_set_detailed_error(
 /*===================*/
 	trx_t*		trx,	/* in: transaction struct */
-	char*	msg);	/* in: detailed error message */
+	const char*	msg);	/* in: detailed error message */
 /*****************************************************************
 Set detailed error message for the transaction from a file. Note that the
 file is rewinded before reading from it. */

innobase/trx/trx0trx.c

@@ -59,7 +59,7 @@ void
 trx_set_detailed_error(
 /*===================*/
 	trx_t*		trx,	/* in: transaction struct */
-	char*	msg)	/* in: detailed error message */
+	const char*	msg)	/* in: detailed error message */
 {
 	ut_strlcpy(trx->detailed_error, msg, sizeof(trx->detailed_error));
 }