if building and running a sketch on a device across multiple machines, the
debug.keystore will be different. when trying to install, you'll get an
error saying that the application must be manually removed.

options for this: 1) copy the keystore between machines that do development
(yech) 2) automatically remove the code the first time it's compiled and
installed from p5 within a session.

#2 is better, but requires a check to see if the application is already
installed. the remove operation seems fairly quick.

on the other hand, the actual 'release' keystore will have to be synched
between machines, so maybe we just need to make it easier to set up a
processing-specific keystore to be used for debug and release.