Fix various issues detected by megacheck (#880)

* Fix various issues detected by megacheck

I've ran honnef.co/go/tools/cmd/megacheck and fixed a few of the
things that came up there.

* Cleanup using Gogland

pkg/proc/proc_unix_test.go

@@ -3,6 +3,7 @@
 package proc_test
 
 import (
+	"fmt"
 	"runtime"
 	"syscall"
 	"testing"
@@ -12,6 +13,15 @@ import (
 	protest "github.com/derekparker/delve/pkg/proc/test"
 )
 
+type errIssue419 struct {
+	pid int
+	err error
+}
+
+func (npe errIssue419) Error() string {
+	return fmt.Sprintf("Pid is zero or negative: %d", npe.pid)
+}
+
 func TestIssue419(t *testing.T) {
 	if testBackend == "lldb" && runtime.GOOS == "darwin" {
 		// debugserver bug?
@@ -20,29 +30,43 @@ func TestIssue419(t *testing.T) {
 	if testBackend == "rr" {
 		return
 	}
+
+	errChan := make(chan error, 2)
+
 	// SIGINT directed at the inferior should be passed along not swallowed by delve
 	withTestProcess("issue419", t, func(p proc.Process, fixture protest.Fixture) {
+		defer close(errChan)
 		_, err := setFunctionBreakpoint(p, "main.main")
 		assertNoError(err, t, "SetBreakpoint()")
 		assertNoError(proc.Continue(p), t, "Continue()")
-		resumeChan := make(chan struct{})
+		resumeChan := make(chan struct{}, 1)
 		go func() {
 			time.Sleep(500 * time.Millisecond)
 			<-resumeChan
 			if p.Pid() <= 0 {
 				// if we don't stop the inferior the test will never finish
 				p.RequestManualStop()
-				p.Kill()
-				t.Fatalf("Pid is zero or negative: %d", p.Pid())
+				err := p.Kill()
+				errChan <- errIssue419{pid: p.Pid(), err: err}
 				return
 			}
 			err := syscall.Kill(p.Pid(), syscall.SIGINT)
-			assertNoError(err, t, "syscall.Kill")
+			errChan <- errIssue419{pid: p.Pid(), err: err}
 		}()
 		p.ResumeNotify(resumeChan)
-		err = proc.Continue(p)
+		errChan <- proc.Continue(p)
+	})
+
+	for i :=0; i<2; i++ {
+		err := <-errChan
+
+		if v, ok := err.(errIssue419); ok {
+			assertNoError(v.err, t, "syscall.Kill")
+			continue
+		}
+
 		if _, exited := err.(proc.ProcessExitedError); !exited {
 			t.Fatalf("Unexpected error after Continue(): %v\n", err)
 		}
-	})
+	}
 }