weapon skill is Unarmed Combat. (Giving Drain Life to secondary attacks is a bit over the top.)
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@9000 c06c8d41-db1a-0410-9941-cceddc491573
335BGGYD3NH4ACHUEZGDXKXXMVL6JMGQ7YPHLTU2256GT2VWV24AC
whichm = MUT_DRAIN_LIFE;
howm = 1;
// Drain Life only works if you're unarmed, so only
// give it if unarmed is your best attacking skill.
skill_type wpn_skill = best_skill(SK_SHORT_BLADES, SK_STAVES);
if ((you.skills[SK_UNARMED_COMBAT] > you.skills[wpn_skill])
&& one_chance_in(14))
{
whichm = MUT_DRAIN_LIFE;
howm = 1;
}