add testcase for #369  Coro::State transfer run-time stack corruption
add 5.8, 5.10 and 5.12 to travis matrix
C: fix issue 370, protect against empty SV magic

HEf_SVKEY might store an empty SV (NULL) since 5.20 for the \0 magic with the ` symbol.
C bump to 1.51_01
Changes: update for 1.51_01
add 371 to testc.sh

usage: t/testc.sh -O3 -q -A 371; gdb --args ./ccode371_o3 -Dt
better issue57 comments on the %hack_xs_detect for Scalar::Util and Params::Util
revise t/testcore fails with 5.21.3d-nt

also update t/CORE/io/layers.t
t/CORE/op/eval.t hangs now with 5.21 (no level), but does not with 5.14
t/testcore.pl: mark regressions from 5.18 and 5.21
t/testcore.pl: mark 5.20 regressions also
1.51_02: word-aligned PV overallocation >5.18, PMOP code_list

1. fixes t/CORE/comp/colon.t regression since 5.18, issue #372
COW Perl_sv_setsv_cow assert(SvCUR(sstr)+1 < SvLEN(sstr))
Fixed by overallocating each static string to at least word alignment.

Note: perl 5.18-5.21.3 itself has a broken overallocation scheme for short strings
(that's why perl5.20.1 disabled COW as performance regression),
because it allocates 10 byte instead of 8 for short strings len < 6.
We use 8 byte instead.

2. add prelim untested code for PMOP code_list, saveoptree for this OP*
t/testcore.pl: update core test results
fix PMOP code_list, fix t/CORE/comp/parser.t >5.16

actually store the PMOP code_list LISTOP (no tree, just one op)

use a compat version of t/CORE/comp/parser.t which works across 5.14-5.21
delete the incompat parts.
core tests: analyze and adjust length (#373), analzye gv.t
core tests: use encoding is deprecated for some uni/*.t: #354
C: protect from warning: Redundant argument in printf

we use 1x the long form and for several sections only the short form
C: protect from warning: Redundant argument in sprintf

and uninitialzed $magic warnings.
5.21 is now much stricter with those warnings.
fix t/CORE/comp/retainedlines.t for 5.20
add t/CORE/comp/hints.t: fails sv_magic assert with <=5.14
t/CORE/op/array.t: fix test

deprecated push(foo, blah) is unsupported since 5.21
and the eval workaround does not work with perlcc.
so disable support for this deprecation