Now, If one or both of the files are too big to show or get the
difference from them, Yobi show an error message different from
one for the case if the difference is oversized.
This also fixes an error have occured when render small diff of an
oversized file because FileDiff.getError returns A_SIZE_EXCEEDED or
B_SIZE_EXCEEDED if the file is larger than the FileDiff.LINE_LIMIT. If
the diff is not larger than the limit, it should be able to rendered
even if the file is larger than the limit but small enough not to raise
And add tests for some exceptional cases.
Add 'lang' field in User model and store user's preferred language every
time user send a request which has Accept-Language HTTP field(s) and/or
language preference in a cookie.
When Yobi send notification emails, it groups recipients by preferred
language and send the email to each group separately in the preferred