bug 28040 Turkish: properly handle dotted and dotless i

bug 28040 Turkish: properly handle dotted and dotless i

As mentioned by Bawolff on code review, r83970 only handled case change
of the first character lacking full strings support.

This patch override the uc and lc methods for the Turkish language (tr)
using preg_replace() which know about unicode. Other possible choices
would have been:
 - strtr() =>  outputs garbage
 - mbstring => can not know we handle turkish and transform i to I!

I have amended the RELEASE-NOTES to reflect this patch.

Some new tests are added as well to cover the regular functions as
well as the specific Turkish overriding. Result in testdox:

LanguageTr
[x] Change case of first char being dotted and dotless i
[x] Language tr lower casing override
[x] Language tr upper casing override
[x] Upper casing of a string with dotted and dot less i
[x] Lower casing of a string with dotted and dot less i