C: detect maybe::next::method

fixes issue 326.
Note that there is no maybe::next equivalent in 5.8, so we just use a NEXT::DISTINCT method
C: improve next::maybe/NEXT detection and testcase a bit

NEXT can have any method name afterwards. Also mark the package and mro
C 1.46_02: max 3x walkall, recursively dump included but not yet dumped packages

at inc_cleanup()
rename %saved to %dumped_package,
fixes issue 340 where IO::Socket::INET6 and its deps are not being dumped,
but this change looks problematic.
C: improve walkall, skip core packages

Still: inc-340 causes these -O3 regressions: 45 68
C inc-i340: improve skip_pkg logic

and observe -fno-warnings.

fixes the 45 and 64 regressions,
but breaks (on 5.18):
  200 run-time utf8 hek
and 46 (-fstash) on 5.14 (hek asserts)
C inc-i340: fix -fstash regressions but still not good enough

all 5.14 tests pass now, 5.18 200 also,
but we got many testcore regressions:
t/C-COMPILED/CORE--base--lex.t                         (Wstat: 1536 Tests: 23 Failed: 6)
  Failed tests:  8-9, 12, 18-19, 22
t/C-COMPILED/CORE--mro--next_edgecases.t               (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--op--closure.t                       (Wstat: 1024 Tests: 23 Failed: 4)
  Failed tests:  10-11, 20-21
t/C-COMPILED/CORE--op--dbm.t                           (Wstat: 1024 Tests: 23 Failed: 4)
  Failed tests:  10-11, 20-21
t/C-COMPILED/CORE--op--inccode.t                       (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--op--length.t                        (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--op--sigdispatch.t                   (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--op--undef.t                         (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--re--charset.t                       (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
t/C-COMPILED/CORE--re--substr.t                        (Wstat: 768 Tests: 23 Failed: 3)
  Failed tests:  17-18, 22
inc-i340: inc cleanup with %dumped_package, add optional -fwalkall

use the real check for %INC cleanup:
%dumped_package (what we really dumped), not %include_package (what we wanted to dump)
do the post walker into an -fwalkall option, which should cause no regressions and fix 340
CC crashes, try to refactor WIP