verifiers: File type for fine-grained signature-verification controlling

Let's provide file type info to the I/O layer. This way verifiers
framework and its users will be able to differentiate files and verify
only required ones.

This is preparatory patch.

Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Ross Philipson <ross.philipson@oracle.com>

grub-core/loader/i386/pc/chainloader.c

@@ -172,8 +172,8 @@ grub_chainloader_cmd (const char *filename, grub_chainloader_flags_t flags)
 
   grub_dl_ref (my_mod);
 
-  grub_file_filter_disable_compression ();
-  file = grub_file_open (filename);
+  file = grub_file_open (filename, GRUB_FILE_TYPE_PCCHAINLOADER
+			 | GRUB_FILE_TYPE_NO_DECOMPRESS);
   if (! file)
     goto fail;