egg-secure-memory: Allocate enough space for the guard pointers
Cell allocations have an overhead of two pointer-sized words, which we need to take into account. Otherwise, whenever we try to allocate a new block to hold at least
DEFAULT_BLOCK_SIZE - 2 * sizeof (void *)bytes, it will end up too small to allocate a cell of that size and we will fall back to non-mlock'd memory with a warning.
egg-secure-memory: Add a warning if #36 happens again
If we call sec_block_create() to allocate a block sized to hold
lengthbytes, and we succeed, then we should really be able to sec_alloc() a cell of
lengthbytes within that block. If we can't, then we chose the size of the block incorrectly.