Fix some compiler warnings introduced in r11619. I checked with

George: ompi_ddt_type_size() returns a signed int only because of the
MPI spec; it will never return a negative value.  So casting the
return value out of it to a (uint32_t) is safe, and makes the
comparisons be between two unsigned values. 

This commit was SVN r11639.

The following SVN revision numbers were found above:
  r11619 --> open-mpi/ompi@8667648a1b

ompi/mca/coll/tuned/coll_tuned_bcast.c

@@ -85,8 +85,12 @@ ompi_coll_tuned_bcast_intra_chain ( void *buff, int count,
         segcount = count;
         num_segments = 1;
     } else {
-        /* segment the message */
+        /* segment the message (ompi_ddt_type_size() will never return
-	if (segsize < typelng) segsize = typelng; /* push segsize up to hold one type */
+           a negative value in typelng; it returns an int [vs. an
+           unsigned type] because of the MPI spec) */
+	if (segsize < ((uint32_t) typelng)) {
+            segsize = typelng; /* push segsize up to hold one type */
+        }
         segcount = segsize / typelng;
         if (segcount > count) { /* we have a single underfilled segment */
             segcount = count;
@@ -276,14 +280,17 @@ ompi_coll_tuned_bcast_intra_split_bintree ( void* buffer,
 
     err = ompi_ddt_type_size( datatype, &type_size );
 
-
-
     /* Determine number of segments and number of elements per segment */
     counts[0] = count/2;
     if (count % 2 != 0) counts[0]++;
     counts[1] = count - counts[0];
     if ( segsize > 0 ) {
-    	if (segsize < type_size) segsize = type_size; /* push segsize up to hold one type */
+        /* Note that ompi_ddt_type_size() will never return a negative
+           value in typelng; it returns an int [vs. an unsigned type]
+           because of the MPI spec. */
+    	if (segsize < ((uint32_t) type_size)) {
+            segsize = type_size; /* push segsize up to hold one type */
+        }
         segcount[0] = segcount[1] = segsize / type_size; 
         num_segments[0] = counts[0]/segcount[0];
         if ((counts[0] % segcount[0]) != 0) num_segments[0]++;
@@ -531,7 +538,6 @@ ompi_coll_tuned_bcast_intra_bintree ( void* buffer,
         comm->c_coll_selected_data->cached_bintree_root = root;
     }
 
-
     err = ompi_ddt_type_size( datatype, &type_size );
 
     /* Determine number of segments and number of elements sent per operation  */
@@ -540,8 +546,12 @@ ompi_coll_tuned_bcast_intra_bintree ( void* buffer,
         segcount = count;
         num_segments = 1;
     } else {
-        /* segment the message */
+        /* segment the message. Note that ompi_ddt_type_size() will
-        if (segsize < type_size) segsize = type_size; /* push segsize up to hold one type */
+           never return a negative value in typelng; it returns an int
+           [vs. an unsigned type] because of the MPI spec. */
+        if (segsize < ((uint32_t) type_size)) {
+            segsize = type_size; /* push segsize up to hold one type */
+        }
         segcount = segsize / type_size;
         if (segcount > count) { /* we have a single underfilled segment */
             segcount = count;