r.king and r.cappallo   july 1977   subroutine montid
evaluation of tidal friction terms in right side of differential
equations for the moon's orbit.  called by morfn, this routine
incorporates m.slade's coding from monfn.
Added indirect terms in partials due to dependence of tidal force on
position and velocity - J.F.Chandler 2007 Nov

ecor  = earth relative to sun (re is distance)
mcor  = moon relative to sun (rm is distance)
mecor = moon relative to earth (rem is distance)
mcor etc. are equatorial coordinates
smcor etc. are selenodetic coordinates

cosphi = ahat(1)*uhat(1) + ahat(2)*uhat(2) + ahat(3)*uhat(3)
if(abs(cosphi).ge.1.) then
sinphi=0.
else
sinphi=sign(sqrt(1. - cosphi**2),
.       uhat(1)*eomga(1) + uhat(2)*eomga(2) + uhat(3)*eomga(3))
endif
bhat1  = -(eomg*coseps - xmagn)*sinphi
bhat2  = (eomg*coseps - xmagn)*cosphi