MANIFEST - add new files (try3.in, try4.in, t/signbit.t)
Makefile.PL - tweak compiler checks (include new check for availability of signbitl)
LongDouble.pm - doc amendements
Changes - update
try2.in - tweaks
try.in - tweaks
LongDouble.xs - cater for absence of signbitl
t/abs.t - additional tests