Document -l on symlinkless file systems

We can rely on -l always being false on platforms that don't support
symlinks:
http://www.nntp.perl.org/group/perl.perl5.porters/2014/03/msg214012.html

(cherry picked from commit ae07d0f95d9614b1ffea793b6ac5f2ffa324cb44)
perlhist: add release date for 5.21.0

(cherry picked from commit c21644471caf57f81699480b56af86541046db78)
fix sv_usepvn_flags's docs

Newx != malloc, mixing Newx and malloc leads to heap corruption on some
builds like Win32, use the official Perl API for allocating memory.

(cherry picked from commit 461a975bd8196c522aeb2e0a06eb6980c25ffa2e)
[perl #121976] - Fix typo in pod

(cherry picked from commit c5e9a8e7dadb9fc0aed0209af0d2dd2fcce6e64a)
PATCH: [perl #121630]: perlpod clarification

(cherry picked from commit 556e7d6c8c0da4161c280ee283d9af0cf8ca31a1)
Unicode::UCD.pm: Pod clarifications and nits

(cherry picked from commit 53cb2385fc91c79c1910180c8af1f00f34b0ba10)
Wrap various pod uses of NUL with C<>

This makes the uses of this consistent in our pods.  Also changed one
use of the word 'buffer' into 'string', the latter being more
appropriate.

(cherry picked from commit 6602b93363649555eb1086b0efd043f7ffa7d0b5)
perlapi: Clarify some instances where NUL is or isn't permitted

Some functions that take a string/length pair can have embedded NULs and
don't have to be NUL terminated; others are the opposite.  This adds
text to clarify the issue.

(cherry picked from commit 30a15352eb3f11a226bd42ec93797b1e778f6e9f)
Correct illegal use of >> in Exporter POD.

Discovered during POD unit tests on release of 5.70 to CPAN.
Also correct AUTHORS and checkAUTHORS.PL email to toddr@cpan.org.
Bump Exporter $VERSION to 5.71.

(cherry picked from commit 2fe8fc108913dacf62b158841e6611c1679c6ab1)
lib/utf8.pm: wrap code examples in pod with C<>

(cherry picked from commit 308a4ae118d0c5ca43889a96b89dd0b5be487b5c)
PATCH: [perl #120386]: av_len documentation

I think I have incorporated everybody's concerns in this patch.

(cherry picked from commit b985ae615210d15bfa67bddb2118de1c02c21935)
perllocale: Wrap some text in C<...>

(cherry picked from commit cb88b78e4b2d13c17e9f4cc808037307f54759b3)
perllocale: Wrap some text in C<...>

(cherry picked from commit fee33030d6e870a9f154c8890ce169b4d7317a3e)
perlapi: Nit, and mention NUL for some functions

This adds the mention of embedded or terminating NULs for some functions
where it wasn't previously indicated.

(cherry picked from commit 417b32ce5913df94c743d210447cc1b0112d59f3)
Document that "exec LIST" and "system LIST" may fall back to the shell on Win32

As noted on p5p [1] and subsequently discussed [2].

The Win32 functions for handling exec() and system() attempt to
specially handle shell builtins by catching spawn failures and
re-attempting the spawn using the shell with the given argument LIST.

If "exec PROGRAM LIST" syntax (or the equivalent for system()) is used,
then only the specified PROGRAM will ever be run (although Perl will
still try the spawn twice on Win32 if PROGRAM doesn't exist or otherwise
can't be executed).

[1] http://www.nntp.perl.org/group/perl.perl5.porters/2014/04/msg214556.html
[2] http://www.nntp.perl.org/group/perl.perl5.porters/2014/04/msg214564.html

(cherry picked from commit 94d4006a6dfdde1becb6ac3d43bd51a5b9ffd95f)
be explicit that SvSetSV() doesn't do set magic

(cherry picked from commit f31006c96d4119fe2bd6e9ae42d2dbec49aa2b2c)
perldiag: Add details about variable length lookbehind

See http://nntp.perl.org/group/perl.perl5.porters/215685

(cherry picked from commit d0a29c363d313dc91fc5bfe71f7a5c525acfed03)
Correct two subtle typos.

Add Michael Bunk to Perl AUTHORS.

For: https://rt.perl.org/Ticket/Display.html?id=122120
(cherry picked from commit 4ee4b74ef884933f33e1c4da87e8437880cec5bd)
perlfunc: clarify our [perl #122132]

(cherry picked from commit 0195d767257fbb19db2d3947dd4ce06b73a41d68)
[perl #116925] discuss modifying an SV's buffer

(cherry picked from commit 21134f66d28b7acf8dde08e536e8b4ee120ea3af)