text/template: say more often that templates are safe for parallel execution

It was said already but apparently not enough times.

Fixes #6985.

LGTM=crawshaw
R=golang-codereviews, crawshaw
CC=golang-codereviews
https://golang.org/cl/86300043

src/pkg/html/template/template.go

@@ -62,6 +62,7 @@ func (t *Template) escape() error {
 
 // Execute applies a parsed template to the specified data object,
 // writing the output to wr.
+// A template may be executed safely in parallel.
 func (t *Template) Execute(wr io.Writer, data interface{}) error {
 	if err := t.escape(); err != nil {
 		return err
@@ -71,6 +72,7 @@ func (t *Template) Execute(wr io.Writer, data interface{}) error {
 
 // ExecuteTemplate applies the template associated with t that has the given
 // name to the specified data object and writes the output to wr.
+// A template may be executed safely in parallel.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
 	tmpl, err := t.lookupAndEscapeTemplate(name)
 	if err != nil {

src/pkg/text/template/doc.go

@@ -20,7 +20,7 @@ The input text for a template is UTF-8-encoded text in any format.
 "{{" and "}}"; all text outside actions is copied to the output unchanged.
 Actions may not span newlines, although comments can.
 
-Once constructed, a template may be executed safely in parallel.
+Once parsed, a template may be executed safely in parallel.
 
 Here is a trivial example that prints "17 items are made of wool".
 

src/pkg/text/template/exec.go

@@ -108,6 +108,7 @@ func errRecover(errp *error) {
 
 // ExecuteTemplate applies the template associated with t that has the given name
 // to the specified data object and writes the output to wr.
+// A template may be executed safely in parallel.
 func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{}) error {
 	tmpl := t.tmpl[name]
 	if tmpl == nil {
@@ -118,6 +119,7 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 
 // Execute applies a parsed template to the specified data object,
 // and writes the output to wr.
+// A template may be executed safely in parallel.
 func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
 	defer errRecover(&err)
 	value := reflect.ValueOf(data)