Port of the programmable signals patch to recent trunk

Also add some additional changes from the SpringPP patch,
and make some other minor changes/fixes.

src/table/settings.ini

@@ -1458,6 +1458,21 @@ from     = 77
 def      = true
 cat      = SC_EXPERT
 
+[SDT_VAR]
+base     = GameSettings
+var      = construction.maximum_signal_evaluations
+type     = SLE_UINT16
+from     = 200
+to       = SL_MAX_VERSION
+def      = 256
+min      = 64
+max      = 4096
+interval = 1
+str      = STR_CONFIG_SETTING_MAX_SIGNAL_EVALUATIONS
+strhelp  = STR_CONFIG_SETTING_MAX_SIGNAL_EVALUATIONS_HELPTEXT
+strval   = STR_JUST_COMMA
+cat      = SC_EXPERT
+
 ; previously ai-new setting.
 [SDT_NULL]
 length   = 1