accessor overwrite warning in CHI with latest Moose 0.84+

[Jonathan Swartz]

I just upgraded Moose/Class::MOP, then found that CHI was outputting a
big stacktrace warning:

You are overwriting a locally defined method (is_subcache) with
an accessor at /Library/Perl/5.8.8/Moose/Meta/Attribute.pm line 584

It appears Moose started checking for this since version 0.84 (June 26).

I've put out a fix release of CHI that eliminates this.

Jon