cleaning and fix for #2255, updated random utility function and hash functions

To investigate #2255 (closed) , I created a function that produces a hash parts of the HXTMesh structure in HXT. Using this function, the hash of the input 2D mesh is now printed at the start of hxtTetMesh().

I also updated and cleaned the code for hashes and LCG inside HXT.

The reproducibility problem for issue #2255 (closed) has been corrected in 3e135257