SQUID_DEFINE_BOOL bug

As Andrew Beverley found:
"
I also found a bug in the current configure.ac. You get the message
"SQUID_DEFINE_BOOL: unrecognized value for USE_LIBNETFILTERCONNTRACK:
'auto'" if you haven't explicitly set with-netfilter-conntrack. This
patch fixes that.
"

I think this is a bug in our implementation of SQUID_DEFINE_BOOL as
matches our tri-state logics.

With our default "everything on unless impossible" policy I believe our
'auto' should be accepted as a value for 'yes'.

Agreed? Opposed?

Amos

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