Electric Fence

A EF_NO_GLOBAL_MALLOC_FREE preprocessor flag was added to work around buggy environments. This prevents malloc(), free(), realloc(), and calloc() from being put into the global namespace of the efence library, thus only files which include efence.h will call the efence malloc() replacement functions. This flag is also helpful where the linking order cannot be controlled, for example when memory is allocated from a library not using efence, but free() is called from using efence. This is a problem when using .dll libraries linked against msvcrt.dll and its malloc/free under MS Windows.