Add support for snapshots

Fixed memory leaks.

  Fix copy code for reals and vectors

  cleanup some FIXMEs

  Clean up the handling of translation from TreeIL types to C types.  There are two cases:
  translating to the external C API amd translating to the internal Diderot types.

  Working on factoring out the generation of code to translate between the internal
  Diderot representation of types (e.g., Diderot_vec3_t) and the external C API
  (e.g., float[3]).

  Working on input support

  Working on input variable support

  Fixed typo

  change back to using the same runtime for both libraries and standalone executables

  Working on library support

  Fixing bugs in generated code

  Working on library support

  more work on library support

  Working on library support

  Working on adding library support to compiler

  add D_Proto to the CLang module

  Create a branch to implement things that we need for the Vis 2012 paper

  Merging changes from pure-cfg branch back into trunk

  Merging in changes from pure-cfg branch.

  Merging in changes from pure-cfg branch: removed CL, expanded trace, and added method name
  datatype.

  merging changes from pure-cfg

  merging changes from pure-cfg

  Added support for hest-based command-line arguments to trunk.  Also switched
  output filename to prog.txt (from mip.txt)

  Porting many changes from the pure-cfg branch, including value numbering
  and support for parallel execution on SMP systems.

  Port updates from development branch to support die.

  more merging of pure-cfg changes back into trunk

  More merging of pure-cfg back into trunk

  Backporting changes from pure-cfg branch.  These include the "actor" ==> "strand"
  changes.

  Working on codegen

  Working on codegen

  Working on coed generation

  Minor edit

  Working on code generator API

  Upated URL in header to diderot-language.cs.uchicago.edu

  Beginnings of code generation infrastructure