cmd: Avoid rereading batch file for every call/goto executed (try 2)

[Octavian Voicu]

2011/9/5 Frédéric Delanoy <frederic.delanoy at gmail.com>:
> +        static WCHAR string[MAX_PATH];

Why make this static? It's only a temporary buffer and it's only used
once, when building the cache.

Octavian