fix a "max-cache-size" configuration bug

fix a "max-cache-size" configuration bug

"max-cache-size default;" is allowed, according to the documentation
and the parser, but when it's configured, named crashes due to an
INSIST that the only legal string value is "unlimited". this has
been fied.

the configuration has also been simplified. previously, we checked for
max-cache-size in view and options, then determined whether to look in
the global default options based on whether the view had recursion set.
the default value set there was only applicable to views with recursion.
now, the default is an explicit "default", which affects views with
and without recursion in different ways.

the cfg type for "max-cache-size" has been changed from
cfg_type_sizeorpercent to cfg_type_maxcachesize.