enable headless snapshotting
add headless mode for packrat::clean
document new dry.run parameter for packrat::clean
bump version
handle already-clean projects gracefully
bump version
pass project to hooks
bump version
Merge branch 'feature/headless-actions'

Conflicts:
	DESCRIPTION
	R/packrat.R
	inst/resources/init.R
Update scenario
fix bad merge
Unload user packrat, load private packrat
Merge branch 'feature/unload-user-packrat' of https://github.com/rstudio/packrat into feature/unload-user-packrat