X.A.Search: Make (!>) right associative
X.A.Search: Make (!>) right associative

Unless specified otherwise, operators in Haskell associative to the
left.  However, the ergonomics of (!>) heavily lean towards the left
operand being a "single" search engine, not a combined one.

This causes trouble when not using `multi` or defining search engines
with a right fold, but (following the documentation) writing something
like

    multiEngine = intelligent (wikipedia !> mathworld !> (prefixAware google))

instead.  This particular definition would force the user to write
`wikipedia/mathworld:wikipedia:search-term` instead of just
`wikipedia:search-term` to access the first search engine.

Simply giving (!>) an explicit associativity fixes these problems.

xmonad/xmonad-contrib,xmonad/xmonad-contrib