Assorted set of small fixes. (#307)

- When the filtering results in an empty list of selected tables, make
    sure we don't enter infinite loop waiting for events that won't happen.

  - Make sure to prepare the pgcopydb_table_size (temporary) table when
    doing the pgcopydb copy ... commands that need it.

  - Ensure proper memory allocation and calloc() error detection when
    printing the summary tables.

  - Work around what looks like a compiler bug when int errors = 0; actually
    sets the errors counter to 32759 on macOs. For that the COPY workers are
	now always in "fail-fast" mode, we can't count the errors anymore.