Skip the ASSIGN directive only when real assignment

[jjatria]

Template::Grammar labels '=>' as an ASSIGN directive.
Since the autofilter skips ASSIGN directives, literal
hashes get incorrectly skipped. This patch makes the
autofilter skip ASSIGN directives only when they use
'='.

This is an attempt at addressing RT #118763.

I'm not sure if this is the correct solution, since it was difficult to find documentation on what the ASSIGN directive is supposed to be. I'll be happy to discuss alternative solutions.