Add memsets after allocation of all Backend implementors.

Now every struct that implements the Backend trait is completely
cleared before we start initialising any of its fields. This will mean
I can add new fields that default to 0 or NULL, without having to mess
around initialising them explicitly everywhere.

otherbackends/raw.c

@@ -156,6 +156,7 @@ static char *raw_init(const BackendVtable *vt, Seat *seat,
     char *loghost;
 
     raw = snew(Raw);
+    memset(raw, 0, sizeof(Raw));
     raw->plug.vt = &Raw_plugvt;
     raw->backend.vt = vt;
     raw->s = NULL;

otherbackends/rlogin.c

@@ -233,6 +233,7 @@ static char *rlogin_init(const BackendVtable *vt, Seat *seat,
     char *loghost;
 
     rlogin = snew(Rlogin);
+    memset(rlogin, 0, sizeof(Rlogin));
     rlogin->plug.vt = &Rlogin_plugvt;
     rlogin->backend.vt = vt;
     rlogin->s = NULL;

otherbackends/supdup.c

@@ -683,6 +683,7 @@ static char *supdup_init(const BackendVtable *x, Seat *seat,
     const char *utf8 = "\033%G";
 
     supdup = snew(struct supdup_tag);
+    memset(supdup, 0, sizeof(Supdup));
     supdup->plug.vt = &fn_table;
     supdup->backend.vt = &supdup_backend;
     supdup->logctx = logctx;

otherbackends/telnet.c

@@ -721,6 +721,7 @@ static char *telnet_init(const BackendVtable *vt, Seat *seat,
     int addressfamily;
 
     telnet = snew(Telnet);
+    memset(telnet, 0, sizeof(Telnet));
     telnet->plug.vt = &Telnet_plugvt;
     telnet->backend.vt = vt;
     telnet->conf = conf_copy(conf);