replace STRING::string() by c_str()

[bertsky]

As of tesseract-ocr/tesseract@cb0c024, Tesseract's API changed. This adapts to that change. I am not at all sure how to check this still builds older Tesseract versions, though. Help is appreciated.

[stweil]

Commit tesseract-ocr/tesseract@4d514d5 added STRING::c_str as an alias for STRING::string in 2013, so it should be available in all relevant versions of Tesseract.

The latest Tesseract code (Git master) removed STRING::string.

That means the commit here should work with all current versions and is required for the latest Tesseract code.

[stweil]

Thank you, @bertsky and @sirfz.

Additional changes will be required in the future because I plan to remove the file strngs.h and the proprietary STRING class from the Tesseract API. It will be replaced either by std::string or by char*.

[sirfz]

Thanks for the info, we should be able to handle that without breaking compatibility for older versions. Please let us know once this change is pushed.

[stweil]

@sirfz, it would help to have a tagged release with this commit.