don't fail in library utility function, return with error code instead and let
application decide what is best on how to proceed

* check whether a library has been loaded before; in this case, don't allocate
  new memory but load from old library again
* vital parameters, previous exit_fun are checked by AssertFatal()
* structure has changed a bit to make it easier to follow (instead of nested
  ifs includes one goto to the end of the function)
* formatting has been improved

LOG_F replaced by LOG_DUMPMSG. Add a generic function to dump a buffer or message. Go on with LOG_M implementation improvement. Remove redundant options to enable/disable logs.