Fix for github issue #23 - sensitivity.analysis start/end date
default to the run's start/end if not explicitly passed.
Merge branch 'master' of git://github.com/PecanProject/pecan into github_23
Fixed typo in last commit where start.date should've been end.date
Merge pull request #29 from TonyCohen/github_23

Fix for issue #23 - sensitivity.analysis start/end date