Let the internal XMS driver use int15 memory and smalloc.
ems.sys can activate it if no other XMS driver is loaded.
Merge old $_xms and $_ext_mem into a single $_xms option.
Correct int15/88 and e801.
ems.sys uses less resident memory if the XMS UMB handler is not hooked.


git-svn-id: https://dosemu.svn.sourceforge.net/svnroot/dosemu/trunk@1448 7758b857-130e-0410-ab9c-d8735a528d18