ogle: allow multi-valued expressions such as regular expressions
Allows us to set a group of breakpoints in a single call.
Clean up expression evaluation a bit (it's still rudimentary).
Fix a bug in breakpoint: need to back up the PC after the trap.
Also fix a silly bug in formatting the startup error in ogleproxy.

Can now trace a simple program using breakpoints.

LGTM=nigeltao
R=nigeltao
https://golang.org/cl/77140045
6 files changed