helpful panics

Godeps/Godeps.json

@@ -197,7 +197,7 @@
 		},
 		{
 			"ImportPath": "github.com/jbenet/goprocess",
-			"Rev": "c5455a611a9e0cebac87e7ae421c3273c3224000"
+			"Rev": "060ad098994e6adac22f0bd889eb756d4f5ad35b"
 		},
 		{
 			"ImportPath": "github.com/kr/binarydist",

Godeps/_workspace/src/github.com/jbenet/goprocess/impl-mutex.go

@@ -35,6 +35,10 @@ func newProcess(tf TeardownFunc) *process {
 }
 
 func (p *process) WaitFor(q Process) {
+	if q == nil {
+		panic("waiting for nil process")
+	}
+
 	p.Lock()
 
 	select {
@@ -48,6 +52,10 @@ func (p *process) WaitFor(q Process) {
 }
 
 func (p *process) AddChildNoWait(child Process) {
+	if child == nil {
+		panic("adding nil child process")
+	}
+
 	p.Lock()
 
 	select {
@@ -61,6 +69,10 @@ func (p *process) AddChildNoWait(child Process) {
 }
 
 func (p *process) AddChild(child Process) {
+	if child == nil {
+		panic("adding nil child process")
+	}
+
 	p.Lock()
 
 	select {