Strip leading and trailing whitespace from open_arg() argument.
Strip leading and trailing whitespace from open_arg() argument.

This fixes the issue of URLs being interpreted as search terms if
entered with additional whitespace.

desyncr/vimprobable,ThomasAdam/vimprobable,desyncr/vimprobable,desyncr/vimprobable,hut/vimprobable,fanglingsu/vimprobable,DeadDork/vimprobable2,DeadDork/vimprobable2,fanglingsu/vimprobable,ThomasAdam/vimprobable,hut/vimprobable,fanglingsu/vimprobable,ThomasAdam/vimprobable,hut/vimprobable,DeadDork/vimprobable2,DeadDork/vimprobable2,desyncr/vimprobable