eina_btlog: allows continuous running on input, flush when possible.

eina_btlog: allows continuous running on input, flush when possible.

eina_btlog will make a table of the backtrace and then must compute
columns length.

However, if not running in such mode (ie: show_compact/-c), we don't
need to queue lines or compute column lengths.

Also, now that we accept non-backtrace lines, like other output
interleaved, then flush the table once such line is found, this will
restart the table columns for the next output, but at least allows
eina_btlog to run on a live output, such as:

       myapp 2>&1 | eina_btlog