Error management and messages

[plecharpent]

In stop an optional arg call. may be used for masking the function call before the message specified in the
stop call

From a user point of view the call is not necessary, the main information is the specific message.
To mask the function call message, the call. = FALSE 1may be used.

From a developer point of view the traceback is useful:

• solution 1: add call. = FALSE to the stop call and use traceback() for getting the trace
• solution 2: use an environment variable to activate the function call display in the stop error message or use options()
  options(stop_call =TRUE) usable from inside functions (see .onAttach to add it)