Don't localize $@ in Perl < v5.14 as it caused $@ to be clobbered.

See https://metacpan.org/pod/release/RJBS/perl-5.18.2/pod/perl5140delta.pod#Exception-Handling

Fixes #14

Not sure if this is the  right way to compare versions, and the string eval feels hackish but I don't see any other way to do the conditional localization.