lib-fts: Add max_length to common filter struct. Reorder fields. The latter is for for imaginary alignment enhancements.

lib-fts: Add prefixing contraction filter. Filters away prefixing contracted words, e.g. "l'homme" -> "homme". Tokens to be filtered must be lower case. Only supports French in this initial version.

lib-fts: fts-filter API changed to have a non-pointer vfuncs variable. The main benefit being that the fts-filter implementations can save a few lines of code.

lib-fts: Added string_t *token to struct fts_filter This makes the work a bit easier for simple filters that don't need any state but want to use a string_t.

lib-fts: Include fts-filter.h in fts-filter-private.h This avoids having to always include them both.

lib-fts: Correct comment in filter internal API.

lib-fts: Removed supports() function from filter API I think the original idea was that this could be used to automatically create filters for many languages, but this probably won't be needed or wanted.

lib-fts: Changed filter's internal APIs to return error_r directly. It's not very safe to store strings allocated from data stack to any permanent structs.

fts: Improve filter error handling. In lib-fts: Move error storage to the generic filter struct level. Change make_utf8 helper to void also. In fts: Add the error argument to _filter() calls.

fts: Change filter API to be able to return errors Modify fts_filter_filter() to return integer status codes. It returns 1 if a token was returned, 0 if it was filtered away and -1 on error.

Initial import for lib-fts. Parts of what this code does was already implemented internally by fts-lucene. lib-fts is intended to be usable for all the FTS backends. The APIs are still going to change a bit, but hopefully not after v2.2.17 release. Mostly written by Teemu Huovila.