Modified the method where Pn/Sn travel times are computed for mantle events. Basically made the convergence behavior more robust and imposed a criterion that C * H < 0.2 where C is the Zhao C parameter and H is the depth of the ray turning point below the Moho.

Removed criterion that mantle gradients had to be >= 0 and replaced it with criterion that C and Cm have to be greater than 1e-6.

Added 5 accessor methods to SlbmInterface (in all 4 languages):

getZhaoParameter() returns several parameters computed during calculation of Pn/Sn travel times, including C, Cm, Vm, H and udSign (see documentation for definitions of these parameters).

getGridLatMin(), getGridLatMax(), getGridLonMin() and getGridLonMax() return the valid range of the Earth model loaded with the loadVelocityModel() call.

Fixed a very subtle bug in QueryProfile. It used to be that interpolation was done on the basis of depth of surrounding grid nodes. Changed so that interpolation is done on the basis of radius, which makes a small difference when the GRS80 ellipsoid is used and Earth radius depends on latitude.