Fix a problem with unrefract under the horizon (below
altCrit). unrefract() would use refractionCorr() instead of using the
linear extrapolation below altCrit. As a result, the context menu
would not pop up correctly on objects below the horizon while using
horizontal coordinates with refraction corrections enabled. The
solution is to use the actual refract() method in fixed-point
iteration to implement unrefract().

Some other changes (like using double instead of dms for
refract/unrefract, and having overloaded methods for dms) were made to
make sure the implementation is fast.

CCMAIL: kstars-devel,