should be single quote here
closes #23: a more informative error message
closes #34: by default the device enables recording
a test case for #34
use RStudio for development
there is no reason to disable tests by default

dev.interactive() is FALSE for non-interactive R sessions by default, but actually we can record plots using pdf() as long as we enable the recording

now the tests are run regardless of the current graphics device
re-indent code
define empty plot calls for R 3.0 (for #35)
fixes #35: use the portable versions of is_par_change(), is.empty() and plot_calls()
I think we should preserve plots made by plot.new() because that is the behavior of all R graphics devices (they produce plot files on plot.new())
par_added() is used nowhere, and we already have is_par_change()
news for #35
issue number of #26
bump version