Add a new registry key to check for the location of MPICH2.

Modules/FindMPI.cmake

@@ -86,6 +86,7 @@ set(_MPI_PACKAGE_DIR
 set(_MPI_PREFIX_PATH)
 if(WIN32)
   list(APPEND _MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH\\SMPD;binary]/..")
+  list(APPEND _MPI_PREFIX_PATH "[HKEY_LOCAL_MACHINE\\SOFTWARE\\MPICH2;Path]")
 endif()
 
 foreach(SystemPrefixDir ${CMAKE_SYSTEM_PREFIX_PATH})