bug#5526: 23.1; (master) - charset.c possible unwise use of alloca(3)

[Chong Yidong]

Vivek Dasmohapatra <vivek@etla.org> writes:

> There are actually 3 other locations where the same thing happens, and the
> allocated blocks are stored in a linked list which you need to walk and
> free (I believe) if you switch over to using xmalloc instead. The attached
> patch should do the right thing.

Actually, after looking at this further, I think we need to use
SAFE_ALLOCA instead of xmalloc.  I've changed the code accordingly.
Thanks for pointing out the additional changes required.  (SAFE_ALLOCA
has a bit more overhead, but I don't see a performance problem after
making this change.)