add test for AWS::S3::Signer, sporadically failing

this reveals (suspected) hash or load order bugs as, even though we
pass a method and content to the constructor, when we call the
content_type attribute sometimes it is defined and sometimes it is
not. run the test multiple times and you will see this behaviour:

	/Volumes/code_partition/AWS-S3 > prove -Ilib t/030_signer.t
	t/030_signer.t .. ok
	All tests successful.
	Files=1, Tests=7,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.30 cusr  0.02 csys =  0.34 CPU)
	Result: PASS

	[leejohnson@lees-macbook-air J1 C2783 10:49:52 * lee/up_test_coverage]
	/Volumes/code_partition/AWS-S3 > prove -Ilib t/030_signer.t
	t/030_signer.t .. 1/?
	#   Failed test 'content_type'
	#   at t/030_signer.t line 32.
	#          got: ''
	#     expected: 'text/plain'
	# Looks like you failed 1 test of 7.
	t/030_signer.t .. Dubious, test returned 1 (wstat 256, 0x100)
	Failed 1/7 subtests

	Test Summary Report
	-------------------
	t/030_signer.t (Wstat: 256 Tests: 7 Failed: 1)
	  Failed test:  4
	  Non-zero exit status: 1
	Files=1, Tests=7,  0 wallclock secs ( 0.02 usr  0.01 sys +  0.37 cusr  0.02 csys =  0.42 CPU)
	Result: FAIL

sometimes the test will pass but raise an uninitialized variable
warning, sometimes that will be absent. so there are clear hash or
load ordering bugs here (tested with perl 5.18)

t/030_signer.t

@@ -0,0 +1,36 @@
+#!perl
+
+use strict;
+use warnings;
+
+use Test::More 'no_plan';
+use FindBin qw/ $Bin /;
+
+use Carp 'confess';
+$SIG{__DIE__} = \&confess;
+
+use_ok('AWS::S3');
+
+my $s3 = AWS::S3->new(
+  access_key_id     => $ENV{AWS_ACCESS_KEY_ID}     // 'foo',
+  secret_access_key => $ENV{AWS_SECRET_ACCESS_KEY} // 'bar',
+  endpoint          => $ENV{AWS_ENDPOINT}          // 'baz',
+);
+
+use_ok('AWS::S3::Signer');
+
+isa_ok(
+	my $signer = AWS::S3::Signer->new(
+		method  => 'HEAD',
+		s3      => $s3,
+		uri     => "http://baz/boz",
+		content => \'hello world',
+	),
+	'AWS::S3::Signer'
+);
+
+is( $signer->content_type,'text/plain','content_type' );
+is( $signer->method,'HEAD','method' );
+is( ${ $signer->content },'hello world','content' );
+
+like( $signer->auth_header,qr/AWS foo:.{28}/,'auth_header' );