chg: send type information via S channel (BC)

Previously S channel is only used to send system commands. It will also be
used to send pager commands. So add a type parameter.

This breaks older chg clients. But chg and hg should always come from a
single commit and be packed into a single package. Supporting running
inconsistent versions of chg and hg seems to be unnecessarily complicated
with little benefit. So just make the change and assume people won't use
inconsistent chg with hg.

contrib/chg/hgclient.c

@@ -237,10 +237,10 b' static void handlesystemrequest(hgclient'
 	ctx->data[ctx->datasize] = '\0';  /* terminate last string */
 
 	const char **args = unpackcmdargsnul(ctx);
-	if (!args[0] || !args[1])
-		abortmsg("missing command or cwd in system request");
-	debugmsg("run '%s' at '%s'", args[0], args[1]);
-	int32_t r = runshellcmd(args[0], args + 2, args[1]);
+	if (!args[0] || !args[1] || !args[2])
+		abortmsg("missing type or command or cwd in system request");
+	debugmsg("run '%s' at '%s'", args[1], args[2]);
+	int32_t r = runshellcmd(args[1], args + 3, args[2]);
 	free(args);
 
 	uint32_t r_n = htonl(r);

mercurial/chgserver.py

@@ -287,13 +287,14 b' class channeledsystem(object):'
     """Propagate ui.system() request in the following format:
 
     payload length (unsigned int),
+    type, '\0',
     cmd, '\0',
     cwd, '\0',
     envkey, '=', val, '\0',
     ...
     envkey, '=', val
 
-    and waits:
+    if type == 'system', waits for:
 
     exitcode length (unsigned int),
     exitcode (int)
@@ -303,8 +304,8 b' class channeledsystem(object):'
         self.out = out
         self.channel = channel
 
-    def __call__(self, cmd, environ, cwd):
-        args = [util.quotecommand(cmd), os.path.abspath(cwd or '.')]
+    def __call__(self, cmd, environ, cwd, type='system'):
+        args = [type, util.quotecommand(cmd), os.path.abspath(cwd or '.')]
         args.extend('%s=%s' % (k, v) for k, v in environ.iteritems())
         data = '\0'.join(args)
         self.out.write(struct.pack('>cI', self.channel, len(data)))