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><td class='sub right'></td></tr></table>
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<tr><td><span title='2019-02-09 00:50:16 -0600'>2019-02-09</span></td><td><a href='/guix/commit/gnu/packages/mpi.scm?id=41313acebf39e04c9ddd0857b8cd8b69991c88c3'>gnu: openmpi: Upgrade to 4.0.0.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2019-02-07 15:46:45 +0100'>2019-02-07</span></td><td><a href='/guix/commit/gnu/packages/mpi.scm?id=b07712bfb13039b3ead57e9f3ca91d4e3ebadd2a'>gnu: openmpi: Add dependency on SLURM.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-31 20:57:22 +0100'>2019-01-31</span></td><td><a href='/guix/commit/gnu/packages/mpi.scm?id=cb85742fa81f0357c7ec021d6188bb31bfaeee14'>gnu: hwloc: Update to 2.0.3.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2019-01-31 20:57:22 +0100'>2019-01-31</span></td><td><a href='/guix/commit/gnu/packages/mpi.scm?id=9dd508458987397567ef650e59f29c59f2ebeb23'>gnu: hwloc@1: Update to 1.11.12.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>