cmdserver: correct doc of channeledoutput

in_ is only used as the source of file attributes.

mercurial/commandserver.py

@@ -23,7 +23,7 b' def log(*args):'
 
 class channeledoutput(object):
     """
-    Write data from in_ to out in the following format:
+    Write data to out in the following format:
 
     data length (unsigned int),
     data