Fixes and cleanup for ph5diff

Fixes concurrency issues in ph5diff that can cause interleaved
output

Fixes an issue where output can sometimes be dropped if it ended
up in ph5diff's output overflow file

Fixes an issue where MPI_Init is called after HDF5 has been
initialized, preventing the library from setting up an MPI
attribute to perform cleanup on MPI_Finalize

Fixes an issue in config/cmake/runTest.cmake where the CMake
logic would try to access an invalid list index if the number
of lines in a test's output and reference files don't match

config/cmake/runTest.cmake

@@ -266,12 +266,22 @@ if (NOT TEST_SKIP_COMPARE)
           endif ()
           math (EXPR _FP_LEN "${len_ref} - 1")
           foreach (line RANGE 0 ${_FP_LEN})
-            list (GET test_act ${line} str_act)
-            list (GET test_ref ${line} str_ref)
-            if (NOT str_act STREQUAL str_ref)
-              if (str_act)
-                set (TEST_COMPARE_RESULT 1)
-                message (STATUS "line = ${line}\n***ACTUAL: ${str_act}\n****REFER: ${str_ref}\n")
+            if (line GREATER_EQUAL len_act)
+              message (STATUS "COMPARE FAILED: ran out of lines in ${TEST_FOLDER}/${TEST_OUTPUT}")
+              set (TEST_COMPARE_RESULT 1)
+              break ()
+            elseif (line GREATER_EQUAL len_ref)
+              message (STATUS "COMPARE FAILED: ran out of lines in ${TEST_FOLDER}/${TEST_REFERENCE}")
+              set (TEST_COMPARE_RESULT 1)
+              break ()
+            else ()
+              list (GET test_act ${line} str_act)
+              list (GET test_ref ${line} str_ref)
+              if (NOT str_act STREQUAL str_ref)
+                if (str_act)
+                  set (TEST_COMPARE_RESULT 1)
+                  message (STATUS "line = ${line}\n***ACTUAL: ${str_act}\n****REFER: ${str_ref}\n")
+                endif ()
               endif ()
             endif ()
           endforeach ()