/(?i)\u0149\u0149/ =~ "\u0149\u0149" doesn't match

How to reproduce:

```
$ LD_LIBRARY_PATH=.libs python

>>> from testpy import *
>>> set_encoding('UTF-8')
>>> set_output_encoding('UTF-8')
>>> x2(u"(?i)\u0149\u0149", u"\u0149\u0149", 0, 2)
FAIL: /(?i)ŉŉ/ 'ŉŉ'
```

It seems that Oniguruma 5.9.5 also has this bug.
