Internal cleanup: KEEP_WRITE and KEEP_READ are now called KEEP_SEND and

KEEP_RECV to better match the general terminology: receive and send is what we
do from the (remote) servers. We read and write from and to the local fs.

lib/multi.c

@@ -1299,13 +1299,13 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
 
       k = &easy->easy_handle->req;
 
-      if(!(k->keepon & KEEP_READ)) {
-        /* We're done reading */
+      if(!(k->keepon & KEEP_RECV)) {
+        /* We're done receiving */
         easy->easy_conn->readchannel_inuse = FALSE;
       }
 
-      if(!(k->keepon & KEEP_WRITE)) {
-        /* We're done writing */
+      if(!(k->keepon & KEEP_SEND)) {
+        /* We're done sending */
         easy->easy_conn->writechannel_inuse = FALSE;
       }