Fix doc and message suggested by Thom Brown
pg_upgrade:  adjust logging to use QUERY_ALLOC lengths

Allows the logging to print the entire text of failed queries, rather
than a truncated version.
Fix core dump in jsonb #> operator, and add regression test cases.

jsonb's #> operator segfaulted (dereferencing a null pointer) if the RHS
was a zero-length array, as reported in bug #11207 from Justin Van Winkle.
json's #> operator returns NULL in such cases, so for the moment let's
make jsonb act likewise.

Also add a bunch of regression test queries memorializing the -> and #>
operators' behavior for this and other corner cases.

There is a good argument for changing some of these behaviors, as they
are not very consistent with each other, and throwing an error isn't
necessarily a desirable behavior for operators that are likely to be
used in indexes.  However, everybody can agree that a core dump is the
Wrong Thing, and we need test cases even if we decide to change their
expected output later.
More regression test cases for json/jsonb extraction operators.

Cover some cases I omitted before, such as null and empty-string
elements in the path array.  This exposes another inconsistency:
json_extract_path complains about empty path elements but
jsonb_extract_path does not.
Add #define INT64_MODIFIER for the printf length modifier for 64-bit ints.

We have had INT64_FORMAT and UINT64_FORMAT for a long time, but that's not
good enough if you want something more exotic, like "%20lld".

Abhijit Menon-Sen, per Andres Freund's suggestion.
merge master