client/gobind: make gobind build again
client/gobind: make gobind build again

Brings factotum and context up-to-date.

No new lint or vet errors.

Change-Id: I0f267e2c9446f1eb72ae631bfe171a823ab475b8
Reviewed-on: https://upspin-review.googlesource.com/5102
Reviewed-by: David Presotto <516b9783fca517eecbd1d064da2d165310b19759@google.com>

upspin/upspin,upspin/upspin