make shell autocomplete more robust

context.go

@@ -15,6 +15,7 @@ import (
 type Context struct {
 	App           *App
 	Command       Command
+	complete      bool
 	flagSet       *flag.FlagSet
 	setFlags      map[string]bool
 	parentContext *Context
@@ -22,7 +23,13 @@ type Context struct {
 
 // NewContext creates a new context. For use in when invoking an App or Command action.
 func NewContext(app *App, set *flag.FlagSet, parentCtx *Context) *Context {
-	return &Context{App: app, flagSet: set, parentContext: parentCtx}
+	c := &Context{App: app, flagSet: set, parentContext: parentCtx}
+
+	if parentCtx != nil {
+		c.complete = parentCtx.complete
+	}
+
+	return c
 }
 
 // NumFlags returns the number of flags set