Removing an Evd.merge in Newring.
Removing the Evd.merge function.

Its semantics was dubious, and it was not used anymore anyway.
Removing the last Evd.diff from Hints.
Removing the Evd.diff function.
Removing dead code from Evd.
Cleaning and documenting Clenv.make_evar_clause
Allow camlp5 to have version numbers like "6.09-exp"
Haskell extraction: put unsafeCoerce type declaration later

When Haskell extraction requires magic type coersion, Coq produces
the following code:

  unsafeCoerce :: a -> b
  #ifdef __GLASGOW_HASKELL__
  import qualified GHC.Base
  unsafeCoerce = GHC.Base.unsafeCoerce#
  #else
  -- HUGS
  import qualified IOExts
  unsafeCoerce = IOExts.unsafeCoerce
  #endif

GHC version 7.6.3 does not allow imports after a type declaration,
and produces this error:

  xx.hs:20:1: parse error on input `import'

(referring to the first import statement above).  This patch moves
the unsafeCoerce type declaration to just after the import statement,
fixing this compile error.
Haskell extraction: use explicit -XMagicHash instead of -fglasgow-exts

When Coq's Haskell extraction needs to use unsafeCoerce, it passes
the -fglasgow-exts option to GHC, but recent versions of GHC warn
against this:

  xx.hs:1:16: Warning:
      -fglasgow-exts is deprecated: Use individual extensions instead

This patch does as the warning suggests, replacing -fglasgow-exts
with the specific option that the extraction needs (-XMagicHash).