[AD] updated os detection for DOS port.

["Henrik Stokseth" <hstokset@xxxxxxxxxx>]

here's patches for the dos port to safely fetch os_version and os_revision.
detection of WinMe has been added. this time patches has been tested. :o)
note: win2k is impossible do detect from pure dos unless i can figure out
how to do VxD calls to the nt-kernel, but docs are rare so i will have to do
some hacking and investigating...

note: the patch to rewrite a check in the exdodgy example showed me that
there might be a use for an os_multitasking flag... if nobody has something
against that i'm going to implement it.

-henrik

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