Addition of ln_loadSample in liblognorm.c/h and the supporting functions in samp.c/h
retain ctx object in getFieldName

The library philosophy is to have this available, e.g. to get hold
of the debug function. I have now declared it as "unused", which is
simpler to change once we actually begin to use it AND should result
in exactly the same code after optimization stage.
doc: add new functuionality to ChangeLog