text/template/parse: mostly roll back the error detection for unmatched right delimiters

It's too late to change this behavior: it breaks templates with minimized JavaScript.

Makes me sad because this common error can never be caught: "{foo}}".
Three cheers for compatibility.

(Leave in a fix to a broken test.)

R=golang-dev, dsymonds, rsc
CC=golang-dev
https://golang.org/cl/13689043

src/pkg/text/template/parse/lex.go

@@ -217,10 +217,6 @@ func lexText(l *lexer) stateFn {
 			}
 			return lexLeftDelim
 		}
-		// Check for right after left in case they're the same.
-		if strings.HasPrefix(l.input[l.pos:], l.rightDelim) {
-			return l.errorf("unmatched right delimiter")
-		}
 		if l.next() == eof {
 			break
 		}

src/pkg/text/template/parse/lex_test.go

@@ -340,8 +340,11 @@ var lexTests = []lexTest{
 		{itemText, 0, "hello-"},
 		{itemError, 0, `comment ends before closing delimiter`},
 	}},
+	// This one is an error that we can't catch because it breaks templates with
+	// minimized JavaScript. Should have fixed it before Go 1.1.
 	{"unmatched right delimiter", "hello-{.}}-world", []item{
-		{itemError, 0, `unmatched right delimiter`},
+		{itemText, 0, "hello-{.}}-world"},
+		tEOF,
 	}},
 }