Test oneliner without double escaping dollar sign

Fix #355

Double escaping '$' for Makefile usage is fine, but
we should not use such a syntax while testing and trying
to run the oneliner output.

This change is 'unescaping' the '$$' to '$' so we can perform
some extra checks while using oneliner.

Otherwise as shown in this example a simple 'my $foo' test will fail.

Note we also have to unescape braces '{{' and '}}' used in dmake...
A better solution would be to produce a Makefile and run it directly.

t/oneliner.t

@@ -8,7 +8,7 @@ chdir 't';
 
 use Config;
 use MakeMaker::Test::Utils;
-use Test::More tests => 16;
+use Test::More tests => 17;
 use File::Spec;
 
 my $TB = Test::More->builder;
@@ -24,20 +24,26 @@ isa_ok($mm, 'ExtUtils::MM_Any');
 sub try_oneliner {
     my($code, $switches, $expect, $name) = @_;
     my $cmd = $mm->oneliner($code, $switches);
+    # unescape Makefile syntax
+    $cmd =~ s{\$\$}{\$}g;
+    $cmd =~ s|\{\{|\{|g; # for dmake
+    $cmd =~ s|\}\}|\}|g;
     $cmd =~ s{\$\(ABSPERLRUN\)}{$perl};
 
     # VMS likes to put newlines at the end of commands if there isn't
     # one already.
     $expect =~ s/([^\n])\z/$1\n/ if $^O eq 'VMS';
 
+    # a better idea would be to create Makefile and run them
     $TB->is_eq(scalar `$cmd`, $expect, $name) || $TB->diag("oneliner:\n$cmd");
 }
 
 # Lets see how it deals with quotes.
 try_oneliner(q{print "foo'o", ' bar"ar'}, [],  q{foo'o bar"ar},  'quotes');
 
 # How about dollar signs?
-try_oneliner(q{$PATH = 'foo'; print $PATH},[], q{foo},   'dollar signs' );
+try_oneliner(q{my $PATH = 'foo'; print $PATH},[], q{foo},   'dollar signs' );
+try_oneliner(q{my %h = (1, 2); print $h{1}},[], q{2},   '%h and $h' );
 
 # switches?
 try_oneliner(q{print 'foo'}, ['-l'],           "foo\n",       'switches' );