from pull request 733

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
org.eclipse.jgit.errors.LargeObjectException.

And add tests for some exceptional cases.

from pull request 732

from pull request 734

from pull request 737

from pull request 676

Make the error handling for FileDiff clearer by introducing getError
and setError method. And fix the bug using them.

from pull request 666

from pull request 646

from pull request 647

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
language.

 When a user try to access forbidden page,
 then redirect to login page and show noti message.

from pull request 644