[svn-r20789] Merged 20724 and 20756 from the trunk to fix HDFFV-7527 concerning

invalid enum value comparisons.

Tested on: h5committest

tools/h5diff/testfiles/h5diff_30.txt

@@ -0,0 +1,9 @@
+dataset: </dset1> and </dset2>
+size:           [6]           [6]
+position        dset1           dset2           difference          
+------------------------------------------------------------
+[ 1 ]          YIN              **INVALID VALUE**
+[ 2 ]          **INVALID VALUE** YIN              
+[ 5 ]          YIN              YANG             
+3 differences found
+EXIT CODE: 1