- Fixed compiler errors in latest TEXTURES code.

GCC and Clang reported errors after pull request #61 was merged in master.

1)
```
/home/edward-san/zdoom/trunk/src/w_wad.h:199:23: error: extra qualification on
      member 'GetLumpName'
        void FWadCollection::GetLumpName(FString &to, int lump) const;
             ~~~~~~~~~~~~~~~~^
```

2)
```
/home/edward-san/zdoom/trunk/src/(other files): error: cannot pass
      non-trivial object of type 'FString' to variadic function; expected type
      from format string was 'char *' [-Wnon-pod-varargs]
```