Undo translation of protocol string 'unpack error'

Undo translation of protocol string 'unpack error'

This string is part of the network protocol, and isn't meant to
be translated into another language.  Clients actually scan for
the string "unpack error " off the wire and react magically to
this information.  If it were translated, they would instead have
a protocol exception, which isn't very useful when there is already
an error occurring.

Change-Id: Ia5dc8d36ba65ad2552f683bb637e80b77a7d92f0
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>