add 5.21.0 to corelist, bump version

(cherry picked from commit 75325e51eae379f247bdee76b5c5432b527e4d53)
Assimilate Module-CoreList part of 2ea3abd479
match Module::CoreList version to perl version

(cherry picked from commit 5dcd9147e968bfec99b1906ad64ed0b49c4b44a0)
update corelist for 5.21.0

(cherry picked from commit 4f2cd4f7a279d0ae5eca7a33f848723a7504eaa8)
update Module::CoreList for 5.21.1

Blunder made in the release of 5.21.0:  Module::CoreList was set to version
5.21.1 instead of 5.21.0.  I've at least temporarily given this commit a
dev version.  Worst case, we do that in 5.21.1 and re-sync in 5.21.2.

(cherry picked from commit 5a534470e5a4dc1ea608889b941dcbd482f34184)
Added core-only version check to Module-CoreList

This should ensure that the versions of Module-CoreList modules
always match the version of perl.

Have to special-case skip for v5.21.1, because rjbs

(cherry picked from commit 4915b61c095597462aef8cf7437320c10954bb6d)
Bring all lines in CoreList.pod under 80 cols

(cherry picked from commit 92c6a5ec9f11d991a91d37e304ca77f7a73aa1f9)
Update Module::CoreList for 5.21.1

(cherry picked from commit 04c0d50048e9a1fc76442f5faa4850b9ba85140c)

(pod/perldelta.pod part skipped)
Update Module::CoreList for 5.21.2

(cherry picked from commit 2901561d6eabdbb1b7d6c7cbf667bbb08778387f)

(pod/perldelta.pod part skipped)
Module::CoreList::TieHashDelta stop massive recursion

On machines with very limited memory, EXISTS calling EXISTS caused a very
high number of C stack frames, magic stack swaps, and Perl call stack
frames leading to memory exhaustion. Turn the recursion into a loop. See
[perl #121974].

(cherry picked from commit 42484eedeb4abcee1d893010daa67c1a42ec6424)
Update Module::CoreList for 5.21.2

(cherry picked from commit 6488e103c9fabe91662d9508930e2eb26e2f718b)
Upped version numbers for ModuleList

(cherry picked from commit 633c51bcc9849e67652e4949bd0a125a1a9d0eca)
Update Module::CoreList for 5.21.3

(cherry picked from commit 46e588907ff561f0b5ebb923f1a81423645845e7)
Module::CoreList version number bump

(cherry picked from commit 5c851aa119b52322e162f3105f7395628dc16737)
Reset Module-CoreList $VERSION to 5.020001, as per e1b8fd4fe5 (lost by d5f415e514)
Update Module-CoreList for 5.20.1

(Excluding %upstream and %bug_tracker portions, which involve modules that
are no longer in blead (e.g. Module-Build) and therefore are not suitable
for committing to blead and then cherry-picking to maint; they will be
committed directly to maint instead.)

(cherry picked from commit 1c6aa017a409609fa72ff9fd264ab682537bf528)
Update Module-CoreList for 5.20.1

(Maint-specific parts that could not be committed to blead and cherry-picked
from there.)
Revert cherry-pick of 5c851aa119 - the bump for the as-yet unreleased 5.21.4

This was only cherry-picked to ease merging the 5.20.1 update into blead
and then cherry-picking it back into maint. It shouldn't be here for the
maint release, though, because 5.21.4 hasn't happened yet.
perldelta - Fill in acknowledgements
perldelta - Last-minute fixes