make_table() now supports generator for headers and lines

The length of lines is now checked line-by-line, during the conversion
of cells values to strings, avoiding calling len() on a generator.
Protection of the invalidation of JSON/XML-RPC Exporters

The unregistration loop generated an exception as it looped on a
dictionary being modified.
Errors killing components of a stopping bundle are now logged

Exceptions are logged instead of raised, as it is unlikely to be handled
by the developer...