* DebuggedProcess method: `PrintGoroutinesInfo` -> `GoroutinesInfo`
* `goroutines` command in command/command.go now responsible for
  printing info.

* Better tracking of current goroutine
* More efficient, eliminates superfluous step syscalls
* Handles concurrency and thread coordination better

This allows greater flexibility for using a port set and determining
whether the wait returned due to a breakpoint or process natural death.

Also refactored code a bit, removed printing functions from proctl
package and inlined them into command.