[perl #118651] don't overwrite $! in readdir()

POSIX expects readdir() to leave errno alone when it reaches end of
directory without an error so that case can be detected.  Do the same
in perl.
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[perl #120635] don't leak semaphores

I was calling semctl() with parameters in the incorrect order
[perl #120384] make hash key quoting compatible between perl and XS

In particular:

- if quotekeys is set all hash keys are now quoted, previously the perl
  code didn't quote "safe" numeric keys

- keys of the form ::foo are now quoted by XS as the perl code always did

- XS code quoted "safe" numbers, while the perl code didn't

- perl code didn't quote strings like "1\x{660}", since \x{660}
  matches \d
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Document ->$#* in perlref
Long verbatim lines in SDBM_File.pm
Note usage compatability of Safefree / Newx and friends
Amend pod_lib.pl to work with miniperl (no dynamic loading)

This is to allow cross-compilation builds to run installperl using a
host miniperl instead of the built Perl binary.
config.ce: Use ~cc~, not ~CC~

This was preventing several things from working properly,
like Errno_pm.PL, which tried to use $Config{cppstdin},
which was not set properly.
Correct URL for github.com mirror of Perl 5 repository.

Add Martin McGrath to AUTHORS.

For: RT #120819
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Porting/corelist-perldelta.pl - Use Module::CoreList in dist/

Ensure that the latest version of Module::CoreList is used when
running the script