Preparation for supporting GHC 7.10

In this commit, I only added some changes which don't require a CPP
conditional:

* Allowed base 4.8.*, deepseq 1.4.*, template-haskell 2.10.* and
  time 1.5.* for testing with GHC 7.10.1 RC1.

* The -fwarn-amp flag will be deprecated in GHC 7.10.

* Prelude now imports `traverse` so I renamed the `traverse` method to
  `trav` in the Agda.Auto.NarrowingSearch.Trav type class.

* Added required FlexibleContexts language extension.
Merge branch 'maint-2.4.2'