text/template: add parenthesized pipelines

text/template: add parenthesized pipelines

This is generally useful but especially helpful when trying
to use the built-in boolean operators.  It lets you write:

{{if not (f 1)}} foo {{end}}
{{if and (f 1) (g 2)}} bar {{end}}
{{if or (f 1) (g 2)}} quux {{end}}

instead of

{{if f 1 | not}} foo {{end}}
{{if f 1}}{{if g 2}} bar {{end}}{{end}}
{{$do := 0}}{{if f 1}}{{$do := 1}}{{else if g 2}}{{$do := 1}}{{end}}{{if $do}} quux {{end}}

[rsc, 2012-03-12 18:07:01]

*** Abandoned ***