Introduce new type-based pool allocator.

	* alloc-pool.c (struct alloc_pool_descriptor): Move definition
	to header file.
	* alloc-pool.h (pool_allocator::pool_allocator): New function.
	(pool_allocator::release): Likewise.
	(inline pool_allocator::release_if_empty): Likewise.
	(inline pool_allocator::~pool_allocator): Likewise.
	(pool_allocator::allocate): Likewise.
	(pool_allocator::remove): Likewise.

From-SVN: r223942