Removed sigsetjmp/longjmp usage for DPMI again. A tiny amount of
assembly can do it more efficiently (saves the sigprocmask syscall
that sigsetjmp makes).


git-svn-id: https://dosemu.svn.sourceforge.net/svnroot/dosemu/trunk@1615 7758b857-130e-0410-ab9c-d8735a528d18