arrgh. reduce could for very small message sizes and proc counts call a linear function

this was implemented using a chain (tree followed with pipeline) by setting the chain fanout to a factor of size etc but the chain datastructure was fixed in length and if exceeded the topo create returned a null which isn't helpfull in cid next function of comdup...
Anyway two fixes, first we do have a real linear function so changed the decision function and second altered the
topo chain create to force chain fanouts of less than 1 to 1 and fanouts bigger than max to max.
next check in will change chain to dynamically allocd array (reallocable) but we shouldn't ever use a chain fanout for a linear tree anyway. 
(lession must rerun all tests for all data sizes when changing decision functions)

This commit was SVN r8662.

ompi/mca/coll/tuned/coll_tuned_decision_fixed.c

@@ -242,8 +242,9 @@ int ompi_coll_tuned_reduce_intra_dec_fixed( void *sendbuf, void *recvbuf,
         segsize = 0;
         fanout = size-1;
 /* when linear implemented or taken from basic put here, right now using chain as a linear system */
-/*         return ompi_coll_tuned_reduce_intra_linear (sendbuf, recvbuf, count, datatype, op, root, comm); */
-        return ompi_coll_tuned_reduce_intra_chain (sendbuf, recvbuf, count, datatype, op, root, comm, segsize, fanout);
+/* it is implemented and I shouldn't be calling a chain with a fanout bigger than MAXTREEFANOUT from topo.h! */
+        return ompi_coll_tuned_reduce_intra_basic_linear (sendbuf, recvbuf, count, datatype, op, root, comm); 
+/*        return ompi_coll_tuned_reduce_intra_chain (sendbuf, recvbuf, count, datatype, op, root, comm, segsize, fanout); */
      } else if (msgsize <= 65536 ) {
         segsize = 32768;
         fanout = 8;

ompi/mca/coll/tuned/coll_tuned_topo.c

@@ -274,11 +274,12 @@ ompi_coll_tuned_topo_build_chain( int fanout,
     rank = ompi_comm_rank(comm);
 
     if( fanout < 1 ) {
-        return NULL;
+        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:topo:build_chain WARNING invalid fanout of ZERO, forcing to 1 (pipeline)!"));
+        fanout = 1;
     }
     if (fanout>MAXTREEFANOUT) {
-        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:topo:build_chain invalid fanout %d bigger than max %d", fanout, MAXTREEFANOUT));
-        return NULL;
+        OPAL_OUTPUT((ompi_coll_tuned_stream,"coll:tuned:topo:build_chain WARNING invalid fanout %d bigger than max %d, forcing to max!", fanout, MAXTREEFANOUT));
+        fanout = MAXTREEFANOUT;
     }
 
     /*