Lowercase version of BackendVtable's displayname.

The current 'displayname' field is designed for presenting in the
config UI, so it starts with a capital letter even when it's not a
proper noun. If I want to name the backend in the middle of a
sentence, I'll need a version that starts with lowercase where
appropriate.

The old field is renamed displayname_tc, to avoid ambiguity.

otherbackends/raw.c

@@ -338,7 +338,8 @@ const BackendVtable raw_backend = {
     .unthrottle = raw_unthrottle,
     .cfg_info = raw_cfg_info,
     .id = "raw",
-    .displayname = "Raw",
+    .displayname_tc = "Raw",
+    .displayname_lc = "raw",
     .protocol = PROT_RAW,
     .default_port = 0,
 };