* wesnoth-mode.el (wesnoth-preprocessor-regexp): 'ifn?def' and 'undef' must

* wesnoth-mode.el (wesnoth-preprocessor-regexp): 'ifn?def' and 'undef' must
  have trailing space.
  (wesnoth-mode-map): Added wesnoth-complete-preprocessor.
  (wesnoth-element-closing, wesnoth-element-opening, wesnoth-element): Removed
  constants.
  (wesnoth-element-closing, wesnoth-element-opening, wesnoth-element): New
  functions.
  (wesnoth-element-completion): Fix `wesnoth-history-list' usage.
  (wesnoth-parent-tag): Rewritten to be more efficient.
  (wesnoth-indent-preprocessor): New function.
  (wesnoth-indent-or-complete): Added preprocessor completion.
  (wesnoth-with-fake-insert): New macro.
  (wesnoth-complete-tag): Partially rewritten.
  (wesnoth-insert-tag): Support inserting preprocessor pairs.
  (wesnoth-nth-pair-position, wesnoth-navigate-element, wesnoth-wml-start-pos,
  wesnoth-indent, wesnoth-determine-context, wesnoth-check-wml,
  wesnoth-check-structure): Updated for new wesnoth-element functions.
  (wesnoth-search-for-matching-tag): Only return non-nil when nesting is
  correct.  Updated for new wesnoth-element functions.
  (wesnoth-jump-to-matching): Support matching #define..#enddef and
  #ifn?def..#endif pairs.
  (wesnoth-find-macro-definitions): Fix a bug where incorrect nesting can
  cause nil openings to be paired with closings, causing errors elsewhere.