Enables unicode tests on travis-ci.
Enables unicode tests on travis-ci.

- Adds `USE_NODATA_BUG` env var which maps to `NANODBC_HANDLE_NODATA_BUG`
  build option. This is required for the version of `sqliteodbc` that is
  installed on `ubuntu:precise`, but only when unicode mode is enabled.
  This issue is resolved in newer versions of `sqliteodbc`.

nanodbc/nanodbc,mcg1969/nanodbc,nanodbc/nanodbc,ChrisBFX/nanodbc,norsync/nanodbc,norsync/nanodbc,ChrisBFX/nanodbc,mcg1969/nanodbc