Is the FreeBSD clock UTC or TAI?

[Darren Pilgrim]

This came up during discussion of leap seconds and why UTC and TAI are 
different.  My question is, does FreeBSD's internal clock use UTC or TAI 
for timekeeping?  That is, is wallclock calculated from an exact count 
of the number of seconds since epoch (TAI), then adjusted with a leap 
seconds table to match UTC, or does it internally use UTC and have code 
to deal with the ambiguous seconds that occur at each leap second?