Add new header gssapi_alloc.h

Add new header gssapi_alloc.h

Contains allocator methods for use with mechanisms and mechglues for
allocations that must be made in one module but freed in another.  On
windows, an allocation made in one module cannot safely be freed in
another using the usual c runtime malloc/free; runtime dll mismatch
will cause heap corruption in that case.  But it is safe to instead
directly use HeapAlloc()/HeapFree() specifying the default process
heap.  For now, this header is not public. If it becomes public
strncpy will need to be used instead of strlcpy.

Signed-off-by: Kevin Wasserman <kevin.wasserman@painless-security.com>
git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25330 dc483132-0cff-0310-8789-dd5450dbe970