Make some variables and functions static when not used outside of a module.
Make variables in headers extern.
Delete the unused db_find_watchpoint() function.
DDB_ONPANIC. Lets user ignore breaks but enter DDB on panic. Intended
for machines where debug on panic is useful, but DDB entry is not,
(public-access console, or terminal-servers which send spurious breaks)
Add new ddb hook, console_debugger(), which decides whether or not to
ignore console ddb requests. Console drivers should be updated to call
console_debugger(), not Debugger(), in response to serial-console
break or ddb keyboard sequence.