Convert setvec into a function that disables/enables ints (init code only
for now, resident code will follow later); cli/sti (disable/enable) are
now macros (inlined).
git-svn-id: https://svn.code.sf.net/p/freedos/svn/kernel/trunk@918 6ac86273-5f31-0410-b378-82cca8765d1b