Fix Perl module Module::Pluggable such that it can find plugins that live in
symlinked directories.

Patch borrowed/adapted from Nixpkgs.

--- Module-Pluggable-5.2/lib/Module/Pluggable/Object.pm   2015-04-08 23:28:48.120164135 -0500
+++ Module-Pluggable-5.2/lib/Module/Pluggable/Object.pm   2015-04-08 23:30:27.032166704 -0500
@@ -164,7 +164,7 @@
         my $sp = catdir($dir, (split /::/, $searchpath));

         # if it doesn't exist or it's not a dir then skip it
-        next unless ( -e $sp && -d _ ); # Use the cached stat the second time
+        next unless ( -e $sp );

         my @files = $self->find_files($sp);

@@ -279,7 +279,7 @@
                              (my $path = $File::Find::name) =~ s#^\\./##;
                              push @files, $path;
                            }
-                      }, $search_path );
+                      }, "$search_path/." );
     }
     #chdir $cwd;
     return @files;></td></tr></table>
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<div class='path'>path: <a href='/guix/log/?id=ea240de4af85ae8ecc0c1afcd4778e01a88e6f5c'>root</a>/<a href='/guix/log/po?id=ea240de4af85ae8ecc0c1afcd4778e01a88e6f5c'>po</a>/<a href='/guix/log/po/guix?id=ea240de4af85ae8ecc0c1afcd4778e01a88e6f5c'>guix</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/po/guix?id=ea240de4af85ae8ecc0c1afcd4778e01a88e6f5c&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-03-14 17:57:27 +0100'>2017-03-14</span></td><td><a href='/guix/commit/po/guix?id=df1292074440b556c9f015b178f4bd6b4297f8d3'>nls: Mark (guix scripts pack) as translatable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* po/guix/POTFILES.in: Add 'guix/scripts/pack.scm'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-31 18:35:29 +0100'>2016-12-31</span></td><td><a href='/guix/commit/po/guix?id=f11c444d440b68c3975c2dcaacb24fa3e0e09c7d'>Add 'guix copy'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/scripts/copy.scm: New file.
* guix/scripts/archive.scm (options-&gt;derivations+files): Export.
* doc/guix.texi (Invoking guix copy): New node.
* Makefile.am (MODULES) [HAVE_GUILE_SSH]: Add guix/scripts/copy.scm.
* po/guix/POTFILES.in: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-19 14:39:34 +0100'>2016-12-19</span></td><td><a href='/guix/commit/po/guix?id=11356d263247554e5e77c1974a47b42efdde4b40'>nls: Update 'fr' translation.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-19 14:37:40 +0100'>2016-12-19</span></td><td><a href='/guix/commit/po/guix?id=452ce949892de9f61bd0a1533d4893d36e064401'>nls: Update 'pt_BR' translation.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-19 14:36:50 +0100'>2016-12-19</span></td><td><a href='/guix/commit/po/guix?id=072ec4cf09df19d7faedbcb4243dbbe81d46dae2'>nls: Update 'da' translation.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-12-04 21:41:50 +0100'>2016-12-04</span></td><td><a href='/guix/commit/po/guix?id=2f1b17b2371f3cd843fcee1068d543437e8d61af'>nls: Update 'da' translation.</a></td><td>Marius Bakke</td></tr>
<tr><td><span title='2016-11-12 13:04:45 +0100'>2016-11-12</span></td><td><a href='/guix/commit/po/guix?id=eda2ad5cd1c40e5dd4b8972111e47265c8fc1db3'>nls: Update 'fr' translation.</a></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-11-06 15:58:14 -0500'>2016-11-06</span></td><td><a href='/guix/commit/po/guix?id=84e6d1519493e8f50c7cfbf44cf8dac493b19d18'>nls: Update 'fr' translation.</a></td><td>Leo Famulari</td></tr>
<tr><td><span title='2016-11-05 15:21:26 -0400'>2016-11-05</span></td><td><a href='/guix/commit/po/guix?id=fa5a3f57275347af6dc3e22d5b35eaaa0cfea219'>nls: Update 'pt_BR' translation.</a></td><td>Leo Famulari</td></tr>
<tr><td><span title='2016-10-23 17:22:18 -0400'>2016-10-23</span></td><td><a href='/guix/commit/po/guix?id=41e94ad50abbf540366c0468c6e49831dd776cbe'>nls: Update 'fr' translation.</a></td><td>Leo Famulari</td></tr>
<tr><td><span title='2016-10-06 18:14:45 +0200'>2016-10-06</span></td><td><a href='/guix/commit/po/guix?id=b282c7819227aaad7fb89f4b9ec3f9809824d176'>nls: Update 'de' translation.</a></td><td>Ludovic Courtès</td></tr>