X.U.Run: Use isPrefixOf in withEmacsLibs
X.U.Run: Use isPrefixOf in withEmacsLibs

The `lisp` and `elpa` lists will simply be the (unqualified) file names.
Thus, if we use isInfixOf and try to require a library with a very short
name (like s.el), other things may be chosen over it.  isPrefixOf,
together with the additional `-`, prevents this from happening.

xmonad/xmonad-contrib,xmonad/xmonad-contrib