Ugh, another bug in install2.r deps
The default argument should be NA, not 'FALSE'.  Consequently, we need to do the type error handling to coerce
logicals strigns to logicals and NA strings to NA.  On the down side this means we use the inconsistent-looking
notation to pass the value --deps TRUE while passing error as a boolean with the flag alone (--error).  On the
upside we can also pass strings like c('IMPORTS', 'DEPENDS').