Use font-lock-preprocessor-face for CPP directives

This also changes to use `font-lock-warning-face` for Git's merge
conflicts annotations (see also a469367).

Note: Users will most likely want to customize
      `font-lock-preprocessor-face` now, as the current default looks
      just like `font-lock-function-name-face`.

This hopefully resolves #154.

Author: hvr

Diff for: NEWS

@@ -20,9 +20,13 @@ See also [[https://github.com/haskell/haskell-mode/compare/v13.06...v13.07][deta
 
 - Remove deprecated `haskell-{hugs,ghci}' modules
 
-- Remove deprecated `turn-on-haskell-font-lock` function
-
-- Improve font-locking of type-signatures in presence of newlines
+- Font-locking changes:
+  - Remove deprecated `turn-on-haskell-font-lock` function
+  - Improve font-locking of type-signatures in presence of newlines
+  - Use `font-lock-preprocessor-face' instead of the previously used
+    `font-lock-warning-face` for CPP directives
+  - Use `font-lock-warning-face` instead  of the previously used
+    `font-lock-preprocessor-face` for Git merge conflict annotations.
 
 - Improvements to `haskell-move-nested' module:
   - Add support for operating on active regions

Diff for: haskell-font-lock.el

@@ -328,10 +328,10 @@ Returns keywords suitable for `font-lock-keywords'."
     (setq keywords
 	  `(;; NOTICE the ordering below is significant
 	    ;;
-            ("^<<<<<<< .*$" 0 'font-lock-preprocessor-face t)
-            ("^=======" 0 'font-lock-preprocessor-face t)
-            ("^>>>>>>> .*$" 0 'font-lock-preprocessor-face t)
-	    ("^#.*$" 0 'font-lock-warning-face t)
+            ("^<<<<<<< .*$" 0 'font-lock-warning-face t)
+            ("^=======" 0 'font-lock-warning-face t)
+            ("^>>>>>>> .*$" 0 'font-lock-warning-face t)
+	    ("^#.*$" 0 'font-lock-preprocessor-face t)
 	    ,@(unless haskell-emacs21-features ;Supports nested comments?
 		;; Expensive.
 		`((,string-and-char 1 font-lock-string-face)))
@@ -648,6 +648,7 @@ Invokes `haskell-font-lock-hook' if not nil."
 
 ;; Local Variables:
 ;; byte-compile-warnings: (not cl-functions)
+;; tab-width: 8
 ;; End:
 
 ;;; haskell-font-lock.el ends here