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

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