Suppress output from background fetch

However, show it when there was an error. This is important for the case that a
fork that you have as a remote was deleted, in which case the command log is the
only way to get notified about that.

pkg/commands/oscommands/cmd_obj.go

@@ -22,6 +22,9 @@ type CmdObj struct {
 	// see StreamOutput()
 	streamOutput bool
 
+	// see SuppressOutputUnlessError()
+	suppressOutputUnlessError bool
+
 	// see UsePty()
 	usePty bool
 
@@ -123,6 +126,18 @@ func (self *CmdObj) StreamOutput() *CmdObj {
 	return self
 }
 
+// when you call this, the streamed output will be suppressed unless there is an error
+func (self *CmdObj) SuppressOutputUnlessError() *CmdObj {
+	self.suppressOutputUnlessError = true
+
+	return self
+}
+
+// returns true if SuppressOutputUnlessError() was called
+func (self *CmdObj) ShouldSuppressOutputUnlessError() bool {
+	return self.suppressOutputUnlessError
+}
+
 // returns true if StreamOutput() was called
 func (self *CmdObj) ShouldStreamOutput() bool {
 	return self.streamOutput