Make php-mode work with Emacs 24.4

Fixed by conditionally loading the cl compatibility package at
compile-time. At the same time replaced the old usages of set-difference
with cl-set-difference, so it's clear that the require 'cl only serves
to work around this specific cc-mode bug.
Special highlighting of $this and self/static

$this (and copied from older php-mode $that) are highlighted with the
constant face instead of plain variable face.

Also, self and static no longer look differently (all keyword face so
those too are now different from other statically called methods).
Fix syntactic analysis for function inside block

Add test case for issue #199

* work in progress - not sure if this fix is good enough *

cc-mode causes trouble because the lambda kwd is also used as keyword
preceeding a block. Some options I see:

* don't use c-lambda-kwds, that breaks tests for issue 19/29/etc, so
  those need a new solution
* insert virtual semicolon after }, that changes nothing for normal
  blocks, but does fix this issue where cc-mode thinks it's a closure
  without ; so detects the line following that as statement-cont
Merge branch 'work/issue-173' into work/20141027-all-merged
Merge branch 'work/issue-201' into work/20141027-all-merged

Conflicts:
	php-mode-test.el
	php-mode.el
Merge branch 'work/issue-199' into work/20141027-all-merged

Conflicts:
	php-mode-test.el
	php-mode.el