(TYPICAL_FAILURE_SIZE): Renamed from MAX_FAILURE_ITEMS.

(TYPICAL_FAILURE_SIZE): Renamed from MAX_FAILURE_ITEMS.
Define it simply as a number.
(DOUBLE_FAIL_STACK, regex_compile): Set the limit at the size
TYPICAL_FAILURE_SIZE specifies, rather than at twice that much.
(re_max_failures): Double the initial values.
(INIT_FAIL_STACK): Use TYPICAL_FAILURE_SIZE so that INIT_FAILURE_ALLOC
counts in the proper units.
(INIT_FAILURE_ALLOC): Increase to 20.
(FAIL_STACK_GROWTH_FACTOR): New macro.
(GROW_FAIL_STACK): Renamed from DOUBLE_FAIL_STACK.
FAIL_STACK_GROWTH_FACTOR controls what ratio to increase size by.