introduce temporary aliases

An alias, that was at least once used with the new "tempalias" will not be
written to saved.cfg.

So, now there are four ways to create aliases:

1) alias (or "=")
  General alias, who's value gets saved at game exit in saved.cfg, and
  restored at the next restart - unless the alias was created at a time,
  where persistidents was zero (usually during execution of the game's own
  config files during startup).

2) const
  Creates an alias, that can not be changed. Makes it harder for users
  to destroy their config.

3) push
  Reassigns an alias with a new value. After "pop", the old value is
  restored. Allows the use of "local" aliases in scripts. Also avoids
  name conflicts.

4) tempalias
  Like "alias", but the value will not be written to saved.cfg.

The commit also changes aliases, written by the engine itself, to "temp":
gametimestart, __getmaprevisions

DOCREF tempalias

source/src/command.h

@@ -11,7 +11,6 @@ struct ident
 {
     int type;           // one of ID_* above
     const char *name;
-    bool isconst;
     union
     {
         int minval;    // ID_VAR
@@ -42,39 +41,41 @@ struct ident
         int defaultval;      // ID_VAR
         float defaultvalf;   // ID_FVAR
      };
-    short context;
-    bool persist;
+    short context;          // one of IEXC_* below
+    bool persist;           // if true, value gets written to saved.cfg on exit; set to true, if it's an ID_ALIAS and the value gets changed
+    bool isconst;           // ID_ALIAS: value may not be overwritten
+    bool istemp;            // ID_ALIAS: if value is changed, "persist" will not be set true
 
     ident() {}
 
     // ID_VAR
     ident(int type, const char *name, int minval, int maxval, int *i, int defval, void (*fun)(), bool persist, int context)
-        : type(type), name(name), isconst(false), minval(minval), maxval(maxval), fun(fun),
-          sig(NULL), action(NULL), defaultval(defval), context(context), persist(persist)
+        : type(type), name(name), minval(minval), maxval(maxval), fun(fun),
+          sig(NULL), action(NULL), defaultval(defval), context(context), persist(persist), isconst(false), istemp(false)
     { storage.i = i; }
 
     // ID_FVAR
     ident(int type, const char *name, float minval, float maxval, float *f, float defval, void (*fun)(), bool persist, int context)
-        : type(type), name(name), isconst(false), minvalf(minval), maxvalf(maxval), fun(fun),
-          sig(NULL), action(NULL), defaultvalf(defval), context(context), persist(persist)
+        : type(type), name(name), minvalf(minval), maxvalf(maxval), fun(fun),
+          sig(NULL), action(NULL), defaultvalf(defval), context(context), persist(persist), isconst(false), istemp(false)
     { storage.f = f; }
 
     // ID_SVAR
     ident(int type, const char *name, char **s, void (*fun)(), void (*getfun)(), bool persist, int context)
-        : type(type), name(name), isconst(false), minval(0), maxval(0), fun(fun),
-          sig(NULL), action(NULL), getfun(getfun), context(context), persist(persist)
+        : type(type), name(name), minval(0), maxval(0), fun(fun),
+          sig(NULL), action(NULL), getfun(getfun), context(context), persist(persist), isconst(false), istemp(false)
     { storage.s = s; }
 
     // ID_ALIAS
     ident(int type, const char *name, char *action, bool persist, int context)
-        : type(type), name(name), isconst(false), minval(0), maxval(0), stack(0),
-          sig(NULL), action(action), executing(NULL), context(context), persist(persist)
+        : type(type), name(name), minval(0), maxval(0), stack(0),
+          sig(NULL), action(action), executing(NULL), context(context), persist(persist), isconst(false), istemp(false)
     { storage.i = NULL; }
 
     // ID_COMMAND
     ident(int type, const char *name, void (*fun)(), const char *sig, int context)
-        : type(type), name(name), isconst(false), minval(0), maxval(0), fun(fun),
-          sig(sig), action(NULL), executing(NULL), context(context), persist(false)
+        : type(type), name(name), minval(0), maxval(0), fun(fun),
+          sig(sig), action(NULL), executing(NULL), context(context), persist(false), isconst(false), istemp(false)
     { storage.i = NULL; }
 };