exp/template: make Set.MustParse* methods return the set.

This brings them into line with the Template.MustParse* methods
and makes it possible to use them in global variable initializations.

R=r
CC=golang-dev
https://golang.org/cl/4798059

src/pkg/exp/template/helper.go

@@ -192,11 +192,12 @@ func (s *Set) ParseTemplateFile(filenames ...string) os.Error {
 
 // MustParseTemplateFile is like ParseTemplateFile but
 // panics if there is an error.
-func (s *Set) MustParseTemplateFile(filenames ...string) {
+func (s *Set) MustParseTemplateFile(filenames ...string) *Set {
 	err := s.ParseTemplateFile(filenames...)
 	if err != nil {
 		panic(err)
 	}
+	return s
 }
 
 // ParseTemplateFiles parses the template files matched by the
@@ -228,11 +229,12 @@ func (s *Set) ParseTemplateFiles(pattern string) os.Error {
 
 // MustParseTemplateFile is like ParseTemplateFiles but
 // panics if there is an error.
-func (s *Set) MustParseTemplateFiles(pattern string) {
+func (s *Set) MustParseTemplateFiles(pattern string) *Set {
 	err := s.ParseTemplateFiles(pattern)
 	if err != nil {
 		panic(err)
 	}
+	return s
 }
 
 // ParseTemplateFile creates a set by parsing the named files,