There are two options, one to dump the true curvilinear fields
         and one local approximation (corresponding to what is measuring
         a sensor?)
         documentation update

 Changes to be committed:
	modified:   Changlog
	new file:   check/gradient/README
	new file:   check/gradient/iin
	new file:   check/gradient/make_grad.csh
	new file:   check/gradient/nms.dat
	new file:   check/gradient/receivers.dat
	new file:   check/gradient/sources.dat
	new file:   check/gradient/yannos.dat
	modified:   doc/modeslib_doc.tex
	modified:   doc/symbol.sty
	modified:   nms/global_main.f90
	modified:   nms/module_modes.f90
	modified:   nms/nms.f90