This allows ODBC drivers to create odbcinst.ini-snippets in
/etc/odbcinst.ini.d/ which will be assembled into
/tmp/etc/odbcinst.ini. /etc/odbcinst.ini is provided as a symlink
pointing to /tmp/etc/odbcinst.ini
Hence the unixODBC-provided PostgreSQL driver was also given an
odbcinst.ini.d snippet.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>