point source values replaced by fillvalue

[jcwarner]

Another reason why the fillvalues give me a headache: Most users place point sources at locations where the u- or v- mask is zero (ie land). During the simulation the model will acuatlly compute a source value at that 'land' location and those transports are used in the simulation. However, when writing his or other output files, the u- or v- values at the psource locations will be repalced with fillvalues. This does not allow the user to check if the correct transport is being introduced into the model. Please negate the fillvalue at locations of the point sources. suggested fix: make up a temporary u/vmask that does not mask the point sources in wrt_his send that temporary mask to nf_fwite3d instead of Grid(ng)%umask.