(cache_system_info): Set os_subtype.
(recreate_heap): Update system information after loading heap.
Don't use data_seg pragma here.
(_heap_init, _heap_term) [_MSC_VER >= 1000]: New functions that
override CRT routines.
into Windows 95, Windows NT, and W32, respectively.
Expand "win" substring in variables referring to Microsoft Windows
constructs into "windows".
Canonicalize header comments to use same terminology.
(allocate_heap): Use VALBITS to determine size of heap.
(allocate_heap) [WINDOWS95]: Conditional code removed.
(sbrk): Use VALMASK instead of an unsigned integer mask.