Depend on wxperl-<key> to avoid version skew with libalien-wxwidgets-perl

Depend on the virtual package wxperl-<key>, provided by
libalien-wxwidgets-perl (>= 0.65+dfsg-3), to avoid version skew between
the packages. (Closes: #757855)

Implementation of get_perl_wx_version et al. by gregor herrmann
<gregoa@debian.org>.