PP code uses of curcop
----------------------

pp_rv2gv
	when a new glob is created for an OPpLVAL_INTRO,
	curcop->cop_line is stored as GvLINE() in the new GP.
pp_bless
	curcop->cop_stash is used as the stash in the one-arg form of bless

pp_repeat
	tests (curcop != &compiling) to warn "Can't x= to readonly value"

pp_pos
pp_substr
pp_index
pp_rindex
pp_aslice
pp_lslice
pp_splice
	curcop->cop_arybase

pp_sort
	curcop->cop_stash used to determine whether to gv_fetchpv $a and $b

pp_caller
	tests (curcop->cop_stash == debstash) to determine whether
	to set DB::args

pp_reset
	resets vars in curcop->cop_stash

pp_dbstate
	sets curcop = (COP*)op

doeval
	compiles into curcop->cop_stash

pp_nextstate
	sets curcop = (COP*)op