Some useful additional functions et. al.

When working on anonymizing a rather large DB, I needed some additional functions that are most probably useful for others too (described in docs/maskingfunctions.md). Also, my first attempt to pg_dump_anon this 40+GB DB lead to an error message (something could not be BAST to bytea... sigh). So I added a small RC check to print out the table the COPY failed for.