Configures the option cvmdata.cache_dir so that subsequent
downloads land at path. The directory is created (recursively) if
it does not exist, and writeability is verified before the option
is committed.
See also
Other cache:
cvm_cache_clear(),
cvm_cache_info(),
cvm_cache_path()
Examples
if (FALSE) { # interactive()
cvm_cache_set_path(tempfile("cvmdata-"))
}