AB and LOH consistency
Biologically, a segment can not be both in allelic balance (AB) and
in loss-of-heterozygosity (LOH) at the same time.
To avoid reporting such inconsistencies, the LOH caller will,
if argument xorCalls=TRUE, never report a segment to be in
LOH if it is already called to be in AB.
However, regardless of of the AB call, a segment is still always
tested for LOH, to check weather the LOH caller is consistent with the
AB caller or not. Thus, in order to distinguish the case where
the AB caller and LOH caller agree from when they disagree,
we report either (AB,LOH)=(TRUE,FALSE) or (TRUE,NA). The former is
reported when they are consistent, and the latter when they are not,
or when the AB caller could not call it.