PR# 17978 Toggling all_classes between true and false in config file eventually crashes compiler

A config file that includes a large number of (Eiffel Software) libraries
with root class ANY initially specifies all_classes="true".  System is
frozen.  Then the config file is changed to specify all_classes="false"
and system is frozen again.  Repeating this toggling of the value of
all_classes over and over eventually (on the 17th compile) crashes the
compiler with a seg fault in {SEARCH_TABLE}.internal_search.

I discovered this when I was trying to track down an incrementality crash 
{CL_TYPE_A}.is_expanded.  I suspect that that crash may be due to the same
underlying cause as the present bug.  My guess is that some counter
(for dynamic types?) may be overflowing.

Added test incr420 for this reproducible incrementality bug.
I marked the test "skip" in the catalog because it takes a long time
(about 50 minutes for me on our Solaris x86 loaner machine) before the
test fails.

Run test incr420.