IndexManager :: NormalizeSearchString - Normalize keyword search string

The function normalizes the keyword search string by removing spaces and all words, which are stop-words. Moreover, capital letters are converted to lower case letters.

In order to perform correct conversion from upper to lower case letters proper locales must be set when the character set contains non-latin1 characters. The proper locale name can be set in the option Language_ISO639_3. Locale names depend on the current machine settings and may differ between platforms (e.g. en-US under windows and en_US under LINUX).

Usually, this function is called from LocateKeywords() or Search(), but it might also be called explicitly from the application.