This is vastly inspired by #1113 and scoof+martins testcase+patch.

Add a new cnt* state "cnt_restart" to do the mandatory restart work,
and to move the restart limit check out of vcl_recv{}, getting rid
of a nasty XXX comment.

Set the explicit 503 when over limit, reset in other cases.

Expand scoof+martins test-case to cover more vcl methods, which
were also affected, but not fixed in their patch.

Fixes	#1113