text/template: handle indirection of nil better

[robpike]

http://play.golang.org/p/uP6pCW3qKT

The crash in the last of the sequences in this program is necessary (we indirect through
a nil pointer while attempting to find  value with which to call a function), but the
error presentation is not helpful to the user.

It would be nice to catch this somehow, at least to show context about where the error
occurred in the template.

Maybe an easy fix. Marking for 1.3Maybe in case that's true. The bare panic here is very
unfortunate.

[robpike]

Comment 1:

This issue was closed by revision 71575a9.

Status changed to Fixed.