Merge branch 'ab/simplify-perl-makefile'

The build procedure for perl/ part has been greatly simplified by
weaning ourselves off of MakeMaker.

* ab/simplify-perl-makefile:
  perl: treat PERLLIB_EXTRA as an extra path again
  perl: avoid *.pmc and fix Error.pm further
  Makefile: replace perl/Makefile.PL with simple make rules

contrib/examples/git-difftool.perl

@@ -13,7 +13,7 @@
 use 5.008;
 use strict;
 use warnings;
-use Error qw(:try);
+use Git::Error qw(:try);
 use File::Basename qw(dirname);
 use File::Copy;
 use File::Find;