Allow File analyzers to direcly pass mime type.

This makes it much easier for protocols where the mime type is known in
advance like, for example, TLS. We now do no longer have to perform deep
script-level magic.

src/analyzer/protocol/rdp/rdp-analyzer.pac

@@ -142,7 +142,7 @@ refine flow RDP_Flow += {
 		                 connection()->bro_analyzer()->GetAnalyzerTag(),
 		                 connection()->bro_analyzer()->Conn(),
 		                 false, // It seems there are only server certs?
-		                 file_id);
+		                 file_id, "application/x-x509-user-cert");
 		file_mgr->EndOfFile(file_id);
 
 		return true;