sam: mark samsave executable

sam generates $home/sam.save for modified files. it expects /sys/lib/samsave to be executable to restore the modified files.
xen: correct print format for long
xen: gotta go fast

use smaller timeouts for sleeps while waiting for xen ether and sd devices to come online. in practice they come up very quickly.
xen: fix boot argv0
xen: delete screen.h from pc that accidentally snuck in. a screen.h for xen framebuffer will be added later.
upas/fs: disable imap mail fetch pipeline due to race

pipeline = 1 with a dovecot imap server causes FETCH and OK responses
get interleaved so some message bodies accidentally get merged together.
disabling it will make fetching mail over imap slower, but it works.