* fhandler_floppy.cc (fhandler_dev_floppy::open): Cast second parameter
	in roundup2 to same size as first parameter to make sure mask size is
	correct.
	* fhandler_process.cc (format_process_maps): Ditto.
	* fhandler_raw.cc (fhandler_dev_raw::dup): Ditto.
	* hookapi.cc (find_first_notloaded_dll): Add cast.
	* spawn.cc (av::fixup): Ditto.
	* wincap.h: Add comment to explain the folowing change.
	(wincapc::page_size): Return size_t.
	(wincapc::allocation_granularity): Ditto.

	* mmap.cc: Throughout, accommodate the fact that AT_ROUND_TO_PAGE isn't
	support on 64 bit at all.
	(class mmap_allocator): New class to allocate mmap slots on x86_64.
	(mmap_alloc): Define global instant of mmap_allocator.
	(mmap64): Call mmap_alloc.alloc on x86_64.
	* heap.cc (eval_start_address): Move heap to 0x6:00000000.  Change
	comment to explain why.
	* mmap.cc (MMAP_STORAGE_LOW): Accommodate above change.