R=r CC=golang-dev https://golang.org/cl/199042
add README explaining how to try the web demos. Fixes #339. R=r CC=barry.d.silverman, bss, vadim https://golang.org/cl/165057
R=r DELTA=23 (5 added, 0 deleted, 18 changed) OCL=35510 CL=35518
special all-nacl.bash and test/run-nacl that run just the tests known to work under nacl. the rest requires closures. fix another bug or two in syscall. R=r DELTA=420 (410 added, 8 deleted, 2 changed) OCL=34882 CL=34907