[vile] Two bugs: &gtmotion crash and bad configure error message

[Jānis Rūcis]

Hi,

I switched from Vim to Vile a few days ago, and since then I've come
across a couple of minor problems:

1) The &gtmotion function will cause a crash on an invalid argument.

2) When configuring Vile with '--with-loadable-filters --with-perl',
the configure script claims it can't find the dlsym function, however,
config.log reveals that it is actually a missing -lperl that makes the
dlsym test fail.