Add option to set stack size for threads

Added the ability to tell TBB what stack size to use for new threads.
This is can be done either at the command line or via the process.options
parameter of the configuration. If no value is given, it defaults to the
system default size. This has no effect on the main thread or a single
threaded program.
Set stack size for additional threads to 10MB

The IB RelVal 10.0 needs 10MB for stack size in order to read the
extremely large graph of edm::HepMCProduct stored in the ROOT file.
Merge pull request #1996 from Dr15Jones/addStackSizeControl

Multithreading fixes -- Add stack size control
Merge remote branch 'origin/CMSSW_7_0_X' into CMSSW_7_0_X