added nohup option to runclaw for batch mode
added NOHUP option to Makefile.common
added nice option to runclaw and Makefile.common so can be run in nohup mode with this niceness.  Also convert nohup and nice from str to bool in runclaw since Makefile passes in string False rather than boolean.
remove debug print statements
removed pdb call
remove & from tail of nohup commands - do not want to put in background in some cases
fixes to runclaw behavior when using nohup and nice parameter
Merge branch 'master' into nohup
to include other PRs that have been merged.

* master:
  Change .f to .f90 in conversion Makefiles
  fixed conversion/Makefile_amrclaw_2d to point to f90 rather than .f files
  allow environment passed in to make_all so they can be set in run_tests.py
Make NICE=None the default in Makefile.common and fix runclaw.py to convert any non-integer to None (including string 'None')
Merge pull request #75 from rjleveque/nohup

Nohup