hdf5_ep

[svn-r22619] 
Purpose:
  HDFFV-8003 - ph5diff (parallel h5diff): daily test failure on ember intermittently during non comparable test file comparison
  HDFFV-7755 - parallel h5diff : hanging on koala intermittently during non comparable test file comparison

Description:
  non-comparable test intermittently hung on koala and ember, but not on jam. it didn't occur until -np reaches 4 or bigger. it occurred once out of many repeated attempts of the same test.
  There was a incorrectly (mistakenly?) duplicated code in MPI section which caused such hang in a certain condition. The test used more processes than other tests, which increased chance to trigger more undone processes, and such process could enter the incorrect code section and wait for wrong pair of send. it explains why it occurred intermittently according to machine condition and using a certain feature. 
  Removed incorrect code which blocked correct code.
  Merged from HDF5 trunk r22618.
  
Tested:
 jam (linux32-LE), koala (linux64-LE), ostrich (linuxppc64-BE), some manually repeated test performed in parallel