use goroutine for handling commands in acceptor to avoid deadlock

The program deadlocks when everyone's trying to send.  The
acceptors were all sending responses to commands, and the
proposers were all trying to send Accept! commands.

ecashin@atala go-getting$ ~/hg/go/bin/go run bpaxos.go -p 3 -a 4 2>&1
...
2013/01/11 21:22:21 proposer2 setting val for proposed number 2 iter 2
acceptor saw proposer2 set value "v0 my name is proposer0"; responding
with biggest:2 val:0xf84003d370
acceptor saw proposer2 set value "v0 my name is proposer0"; responding
with biggest:2 val:0xf84003d370
2013/01/11 21:22:21 proposer2 setting val for proposed number 2 iter 3
2013/01/11 21:22:21 proposer1 setting val for proposed number 1 iter 1
throw: all goroutines are asleep - deadlock!

goroutine 1 [chan receive]:
main.main()
        /Users/ecashin/git/go-getting/bpaxos.go:195 +0x370

goroutine 2 [syscall]:
created by runtime.main
        /Users/ecashin/hg/go/src/pkg/runtime/proc.c:225

goroutine 3 [chan send]:
main.(*acceptor).accept(0xf84003d240, 0xf84005b060, 0x0, 0x0)
        /Users/ecashin/git/go-getting/bpaxos.go:168 +0x129
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:189 +0x2a5

goroutine 4 [chan send]:
main.(*acceptor).accept(0xf84003d250, 0xf84005b060, 0x0, 0x0)
        /Users/ecashin/git/go-getting/bpaxos.go:168 +0x129
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:189 +0x2a5

goroutine 5 [chan send]:
main.(*acceptor).accept(0xf84003d260, 0xf84005b060, 0x0, 0x0)
        /Users/ecashin/git/go-getting/bpaxos.go:168 +0x129
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:189 +0x2a5

goroutine 6 [chan send]:
main.(*acceptor).accept(0xf84003d270, 0xf84005b060, 0x0, 0x0)
        /Users/ecashin/git/go-getting/bpaxos.go:168 +0x129
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:189 +0x2a5

goroutine 8 [chan send]:
main.(*proposer).propose(0xf84003a480, 0x4, 0xf84005b060,
0xf84005b000, 0x0, ...)
        /Users/ecashin/git/go-getting/bpaxos.go:106 +0x804
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:192 +0x32d

goroutine 9 [chan send]:
main.(*proposer).propose(0xf84003a4a0, 0x4, 0xf84005b060,
0xf84005b000, 0x0, ...)
        /Users/ecashin/git/go-getting/bpaxos.go:106 +0x804
created by main.main
        /Users/ecashin/git/go-getting/bpaxos.go:192 +0x32d
exit status 2
ecashin@atala go-getting$