allow mnemonics for execution context levels

scriptcontext and isolatecontext now allow plain text mnemonics for
context level arguments (one of CORE, CFG, PROMPT, MAPCFG, MDLCFG)

also:

- cleanup (some dead code and dead prototypes removed)
- some stuff renamed
- script errors now show context levels
- conc is no longer thread-safe (but slightly faster)

DOCREF scriptcontext isolatecontext

source/src/worldlight.cpp

@@ -438,11 +438,3 @@ void freeblock(block *&b)
     if(b) { freeblockp(b); b = NULL; }
 }
 
-block *duplicateblock(const block *s)
-{
-    size_t len = sizeof(block) + s->xs * s->ys * sizeof(sqr);
-    block *b = (block *)new uchar[len];
-    memcpy(b, s, len);
-    return b;
-}
-