text/template: rename the method Template.Template to Template.Lookup

Calling it Template makes it clumsy to embed the type, which html/template
depends on.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/5432079

src/pkg/text/template/exec_test.go

@@ -677,7 +677,7 @@ func TestTree(t *testing.T) {
 	}
 	const expect = "[1[2[3[4]][5[6]]][7[8[9]][10[11]]]]"
 	// First by looking up the template.
-	err = tmpl.Template("tree").Execute(&b, tree)
+	err = tmpl.Lookup("tree").Execute(&b, tree)
 	if err != nil {
 		t.Fatal("exec error:", err)
 	}

src/pkg/text/template/template.go

@@ -136,9 +136,9 @@ func (t *Template) Funcs(funcMap FuncMap) *Template {
 	return t
 }
 
-// Template returns the template with the given name that is associated with t,
+// Lookup returns the template with the given name that is associated with t,
 // or nil if there is no such template.
-func (t *Template) Template(name string) *Template {
+func (t *Template) Lookup(name string) *Template {
 	return t.tmpl[name]
 }