Revert "Use dropWhileEndLE p instead of reverse . dropWhile p . reverse"

This reverts commit 2a8856884de7d476e26b4ffa829ccb3a14d6f63e.
Use dropWhileEndLE p instead of reverse . dropWhile p . reverse

Summary: Using `dropWhileEndLE` tends to be faster and easier to read
than the `reverse . dropWhile p . reverse` idiom. This also cleans up
some other, nearby, messes. Fix #9616 (incorrect number formatting
potentially leading to incorrect numbers in output).

Test Plan: Run validate

Reviewers: thomie, rwbarton, nomeata, austin

Reviewed By: nomeata, austin

Subscribers: simonmar, ezyang, carter, thomie

Projects: #ghc

Differential Revision: https://phabricator.haskell.org/D259

GHC Trac Issues: #9623, #9616

Conflicts:
	compiler/basicTypes/OccName.lhs
rts/PrimOps.cmm: follow '_static_closure' update

Caught by UNREG build failure:

      rts_dist_HC rts/dist/build/PrimOps.o
    /tmp/ghc8613_0/ghc8613_2.hc: In function 'cf8_entry':

    /tmp/ghc8613_0/ghc8613_2.hc:1942:13:
         error: 'base_ControlziExceptionziBase_nestedAtomically_static_closure' undeclared (first use in this function)
         R1.w = (W_)&base_ControlziExceptionziBase_nestedAtomically_static_closure;
                     ^

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Really fix dropWhileEndLE commit

which I fixed before, but failed to pass -a to "git commit --amend"
More progress

There is a mysterious point in TcInteract.kick_out that
I must discuss with Dimitrios
Merge remote-tracking branch 'origin/master' into wip/new-flatten-skolems-Aug14