Oracle: date/time: Fix writing of mismatched c/sql type.

[detule]

There is more information in #959. The condensed story is:

• OEM and PRO oracle drivers exhibit different sensitivities when writing buffers of c type that doesn't exactly match the target sql type. Think writing character buffers to Oracle::DATE targets, for example.
• The SQLBindParameters API call has two types (target parameter SQL type, and buffer C type), and two buffer sizes (target parameter size, and buffer size). It is important that these are specified correctly since it seems some drivers are more flexible than others (if we correctly specify the c type, the buffer length is inferred correctly in some cases, and not in others).
• This PR attempts to:
  • Respect the fact that both OEM and PRO drivers map the Oracle::DATE type to the ODBC SQL_TYPE_TIMESTAMP.
  • Patch the more generic nanodbc code so that the buffer length argument to the SQLBindParameter API call is correctly reported.

This last bullet point in particular, is in the codepath used by other drivers, and all other databases so we need to make sure:

• All unit tests pass

• The nanodbc maintainers don't think that the change is a bad idea.

Closes #962 #959

[simonpcouch]

Looking good!