Import reduced tree patch

http://www.tt-forums.net/viewtopic.php?p=890778#p890778

Update to recent trunk, use extended savegame framework.
Add setting help text, tweak setting name.
Pre-calculate tree growth probabilities.

src/table/settings.ini

@@ -2744,6 +2744,20 @@ strval   = STR_JUST_COMMA
 cat      = SC_BASIC
 patxname = ""everest_treeline.construction.trees_around_snow_line_range""
 
+[SDT_VAR]
+base     = GameSettings
+var      = construction.tree_growth_rate
+type     = SLE_UINT8
+guiflags = SGF_MULTISTRING
+def      = 0
+min      = 0
+max      = 3
+str      = STR_CONFIG_SETTING_TREE_GROWTH
+strhelp  = STR_CONFIG_SETTING_TREE_GROWTH_HELPTEXT
+strval   = STR_CONFIG_SETTING_TREE_GROWTH_NORMAL
+cat      = SC_BASIC
+patxname = ""reduced_tree_growth.construction.tree_growth_rate""
+
 [SDT_VAR]
 base     = GameSettings
 var      = game_creation.custom_sea_level