Improve support for text siglen including underscore

Change-Id: I86204f2aae32834e1592335dca83f40cbf46f559
diff --git a/t/tar_builder.t b/t/tar_builder.t
index 9413440..9cff269 100644
--- a/t/tar_builder.t
+++ b/t/tar_builder.t
@@ -33,10 +33,10 @@
 ok($tar_read->contains_file('example2.xml'), 'File exists');
 
 my $content = $tar_read->get_content('example1.xml');
-like($content, qr!ART_ABC\.00001!, 'Content is correct');
+like($content, qr!A_RT_ABC\.00001!, 'Content is correct');
 
 $content = $tar_read->get_content('example2.xml');
-like($content, qr!ART\/ABC\.00001!, 'Content is correct');
+like($content, qr!A_RT\/ABC\.00001!, 'Content is correct');
 
 
 
@@ -74,10 +74,10 @@
   ok($tar_read->contains_file('example2.xml'), 'File exists');
 
   $content = $tar_read->get_content('example1.xml');
-  like($content, qr!ART_ABC\.00001!, 'Content is correct');
+  like($content, qr!A_RT_ABC\.00001!, 'Content is correct');
 
   $content = $tar_read->get_content('example2.xml');
-  like($content, qr!ART\/ABC\.00001!, 'Content is correct');
+  like($content, qr!A_RT\/ABC\.00001!, 'Content is correct');
 }
 else {
   diag 'Archive::Tar::Builder not installed.';