Force $_cpu_emu="full", and do not crash, if %cs is not saved for signal
handlers on x86-64 (kernels < 2.6.15, #1713659).


git-svn-id: https://dosemu.svn.sourceforge.net/svnroot/dosemu/trunk@1789 7758b857-130e-0410-ab9c-d8735a528d18