html/template: Clarifying references to "text/template" in the documentation.
html/template: Clarifying references to "text/template" in the documentation.

Fixes issue 4634.

R=adg, kevlar
CC=golang-dev
https://codereview.appspot.com/7066053

gnanderson/go,gnanderson/go,gnanderson/go,apparentlymart/golang,tv42/old-go,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,dsriram/golang,tv42/old-go,gnanderson/go,apparentlymart/golang,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,tv42/old-go,dsriram/golang,gnanderson/go,tv42/old-go,gnanderson/go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,apparentlymart/golang,apparentlymart/golang,tv42/old-go,dsriram/golang,dsriram/golang,apparentlymart/golang