We need to read the entire contents of the CLOB in Oracle backend and
not just the number of bytes corresponding to its length in characters
as returned by OCILobGetLength() because this may (and will) be strictly
less than its full size in bytes for any encoding using multiple bytes
per character, such as the de facto standard UTF-8.
Also make reading CLOBs more efficient by doing what Oracle
documentation suggests and using the LOB chunk size for reading.
Finally, add a unit test checking that using non-ASCII strings in UTF-8
(which had to be enabled for the CI) with CLOBs does work.
This commit is best viewed ignoring whitespace-only changes.
5e9f200001