pidgin-with-plugins: fix version number placement in pkg name

Currently the pidgin plugins wrapper is named
"pidgin-VERSION-with-plugins". Fix it so that it becomes
"pidgin-with-plugins-VERSION".

(And add missing newline at the end of file.)
pidgin-with-plugins: rename attrname pidginWrapper -> pidgin-with-plugins

So that both attrname and pkgname is the same. The wrapper was added
just ~1 week ago, so I don't think we need to keep the old name around
for backward compatibility.