Emit (crude) intermediate code for Chemora.

[dmkoppelman]

Currently, Kranc can generate Cactus thorns compatible with
CaKernel. For the Kranc trunk version it generates thorns compatible
with template gpu_cuda/3dblock, for my branch it generates thorns
compatible with gpu_cuda_dc/3dblock2.

In this issue modify Kranc so that it generates thorns compatible both
with the gpu_cuda_dc/3dblock2 template and with the new Chemora code
generation system (see GBS12 Ticket 128).

The generated thorn will have a new file, Chemora.h, in the src
directory. Chemora.h contains intermediate-form code corresponding to
the EDL or Kranc script. When the Startup.cc code is executed
(something which is currently placed in the thorn's src directory) the
intermediate-form code in Chemora.h will be passed to Chemora.

The intermediate-form code is passed to Chemora by a series of
function calls. Crude but quick.

Here are the major changes to Kranc:

Most of the generation of intermediate form code is performed in
CodeGenCalculation.m. Pre-definitions, grid function loads and stores,
and differencing operations are converted into C function calls (what
I'll all intermediate form) and collected on Calculation key reference
ChemoraContents. In KrancThorn.m ChemoraContents is written to new
file Chemora.h, where the intermediate code is wrapped in a procedure
named chemora_cg_thorn_startup. The Startup.cc file is modified to
call chemora_cg_thorn_startup.

Differencing Operations (changes to Differencing.m)
DifferencingProcessCode will now provide the differencing operations
in two forms, as strings (the current method), for existing key
PreDefinitions; and as MMA expressions, for new key
PreDefinitionsExpr.

New function chemoraPrecomputeDerivatives provides information
about each use of a differencing operation.

Consider this a quick-and-dirty first try. I expect that as I
understand Kranc better I'll generate the intermediate code for
Chemora at places that are more appropriate.