adjust $DB::deep from 100 to 1000

adjust $DB::deep from 100 to 1000

$DB::deep defaults to 100; this means that when the debugger gets 100
levels deep in subroutine calls, it automatically breaks execution.
While this might have been appropriate in 1989, in modern Perl programs,
the debugger might break before the program is even compiled.

This patch adjusts the default value up to 1000.

I was not able to find the default value documented anywhere.