netrender fixes:

slave use output log option correctly
use os.path.join more consistently (reported by Dalai Felinto)
unify frame range (was 4 digits on master, 6 elsewhere, now 6 everywhere).
Fix occasional broken pipe between master and slave (didn't affect result, just polluted log).

release/scripts/io/netrender/operators.py

@@ -205,6 +205,7 @@ class RENDER_OT_netclientstatus(bpy.types.Operator):
             conn.request("GET", "/status")
 
             response = conn.getresponse()
+            response.read()
             print( response.status, response.reason )
 
             jobs = (netrender.model.RenderJob.materialize(j) for j in eval(str(response.read(), encoding='utf8')))
@@ -306,6 +307,7 @@ class RENDER_OT_netclientslaves(bpy.types.Operator):
             conn.request("GET", "/slaves")
 
             response = conn.getresponse()
+            response.read()
             print( response.status, response.reason )
 
             slaves = (netrender.model.RenderSlave.materialize(s) for s in eval(str(response.read(), encoding='utf8')))
@@ -354,6 +356,7 @@ class RENDER_OT_netclientcancel(bpy.types.Operator):
             conn.request("POST", cancelURL(job.id))
 
             response = conn.getresponse()
+            response.read()
             print( response.status, response.reason )
 
             netsettings.jobs.remove(netsettings.active_job_index)
@@ -380,6 +383,7 @@ class RENDER_OT_netclientcancelall(bpy.types.Operator):
             conn.request("POST", "/clear")
 
             response = conn.getresponse()
+            response.read()
             print( response.status, response.reason )
 
             while(len(netsettings.jobs) > 0):
@@ -412,6 +416,7 @@ class netclientdownload(bpy.types.Operator):
             for frame in job.frames:
                 client.requestResult(conn, job.id, frame.number)
                 response = conn.getresponse()
+                response.read()
 
                 if response.status != http.client.OK:
                     print("missing", frame.number)
@@ -419,7 +424,7 @@ class netclientdownload(bpy.types.Operator):
 
                 print("got back", frame.number)
 
-                f = open(netsettings.path + "%06d" % frame.number + ".exr", "wb")
+                f = open(os.path.join(netsettings.path, "%06d.exr" % frame.number), "wb")
                 buf = response.read(1024)
 
                 while buf: