Implement [lock_view] and [unlock_view] WML actions

They are trivial wrappers for the wesnoth.lock_view() function in Lua.
Neither takes any parameters.

There is no wrapper for wesnoth.view_locked() yet until I decide on its
name and usefulness factor.

changelog

@@ -273,6 +273,9 @@ Version 1.11.0-svn:
    * [scroll_to] and [scroll_to_unit] now accept an optional boolean immediate=
      attribute (defaults to false) specifying whether to ignore the scroll
      speed setting in Preferences and instantly warp to the selected location
+   * Added [lock_view] and [unlock_view] WML actions, for locking and unlocking
+     gamemap view scrolling (so the user cannot scroll, while WML/Lua actions
+     still can, i.e. for cutscenes)
  * Miscellaneous and bug fixes:
    * Fix wrong preferences path suffix (1.1 instead of 1.10) on Linux and other
      platforms using XDG layout (no compiled-in preferences path override,

data/lua/wml-tags.lua

@@ -359,6 +359,14 @@ function wml_actions.scroll_to_unit(cfg)
 	wesnoth.scroll_to_tile(u.x, u.y, cfg.check_fogged, cfg.immediate)
 end
 
+function wml_actions.lock_view(cfg)
+	wesnoth.lock_view(true)
+end
+
+function wml_actions.unlock_view(cfg)
+	wesnoth.lock_view(false)
+end
+
 function wml_actions.select_unit(cfg)
 	local u = wesnoth.get_units(cfg)[1]
 	if not u then return end