runtimes/google/ipc: switch to using verror2.
runtimes/google/ipc: switch to using verror2.

- use verror2 in ipc.Client, but don't yet change
the return types for StartCall, Finish etc.
- this makes extensive use of local verror2 definitions
in an attempt to support internationalization of 'detailed'
error messages without bloating the number of public ones.

Change-Id: I998db3c72001fb1683751ec55f941411197a46cb

vanadium/go.v23,vanadium/go.v23,vanadium/go.v23