riched20: Add tests for ITextRange interface.

[Caibin Chen]

ITextRange will be used in both richole.c and txtsrv.c. I'm planning
to add more tests in it. I think it makes more sense to have one test
file for each interface, which improves the readability of tests.

2013/7/18 Nikolay Sivov <bunglehead at gmail.com>:
> On 7/18/2013 20:28, Caibin Chen wrote:
>>
>> Add tests for start and end point, setting and getting text.
>> ---
>>   dlls/riched20/tests/Makefile.in |   3 +-
>>   dlls/riched20/tests/txtrng.c    | 343
>> ++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 345 insertions(+), 1 deletion(-)
>>   create mode 100644 dlls/riched20/tests/txtrng.c
>
> You could just use existing file, richole.c fits I think.
>