ParseXS: add comment at the top of all t/5xx*.t

Add a boilerplate comment line or two explaining the purpose of each
file.

dist/ExtUtils-ParseXS/t/501-typemaps-compile.t

@@ -1,4 +1,8 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+# check it built ok.
+
 use strict;
 BEGIN {
 	$|  = 1;

dist/ExtUtils-ParseXS/t/510-typemaps-bare.t

@@ -1,4 +1,8 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+# [ XXX I'm not clear what 'bare' refers to in the test file name ]
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/511-typemaps-whitespace.t

@@ -1,4 +1,8 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+# Check that leading white space in typemap lines are handled correctly.
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/512-typemaps-file.t

@@ -1,4 +1,8 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+# check creating and writing typemaps
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/513-typemaps-merge.t

@@ -1,4 +1,7 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps::merge()
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/514-typemaps-embed.t

@@ -1,4 +1,7 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps::as_embedded_typemap()
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/515-typemaps-cmd.t

@@ -1,4 +1,7 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps::Cmd::embeddable_typemap()
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/516-typemaps-clone.t

@@ -1,4 +1,7 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps::clone()
+
 use strict;
 use warnings;
 

dist/ExtUtils-ParseXS/t/517-typemaps-targetable.t

@@ -1,4 +1,8 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+# test targetable() and targetable_legacy() methods
+
 use strict;
 use warnings;
 use Carp;

dist/ExtUtils-ParseXS/t/518-typemaps-compat.t

@@ -1,13 +1,16 @@
 #!/usr/bin/perl
+#
+# Test ExtUtils::Typemaps:
+#
+# This test file is for making sure that the new EU::Typemaps
+# based typemap merging produces the same result as the old
+# EU::ParseXS code.
+
 use strict;
 use warnings;
 
 use Test::More;
 
-# This test is for making sure that the new EU::Typemaps
-# based typemap merging produces the same result as the old
-# EU::ParseXS code.
-
 use ExtUtils::Typemaps;
 use ExtUtils::ParseXS::Utilities qw(
   C_string