interactive: don't forget to eat the initial event!

seems to be the cause of the synchronization bug we've been
having.
debug: create more informative error messages.
don't ignore MainSync's error!
cfg: implement method to build CFG of a single function.

by the address, which gets around the issue of whether does or
does not want the symbol name to be mangled.
cmd: slightly improved error messages for CFG building issues.
cfg: add a go frontend to build CFG from an address.
cmd: use cfg.FromAddress all over instead of cfg.Local.

FromAddress is more reliable, and usually much quicker too.
cfg: delete debug prints.
cmd: get rid of a superfluous check / unindent code.

the if was always true, and the whole approach would be broken
otherwise.
cmd: extend 'boundid' loop detection to work on a real program.