Upgrade to Lucene 6.4.1 in jena-text and jena-spatial (JENA-1250)

[osma]

These two commits will upgrade jena-text and jena-spatial to use Lucene 6.4.1 (and spatial4j 0.6).

Things to note:

• The Lucene index format is incompatible. Old indexes need to be recreated. There is no backward compatibility, since we are going two major versions up and Lucene generally supports only the index format of the previous major version.
• The multilingual analyzer has been reimplemented to use a different field layout where every language gets a separate field (e.g. label_en, label_fr) as well as a single generic field (label). This had to be done due to API changes in Lucene 5 that made it impossible to use the old mechanism where a single field was used for all languages.

[osma]

I've tested this briefly.

• Unit tests pass for both jena-text and jena-spatial
• I can create a text index and query it normally
• I can create a spatial index and query it normally
• jena.textindexer seems to work
• jena.textindexdump seems to work
• jena.spatialindexer seems to work
• jena.spatialindexdump seems to work

If I try to use a text index created before the Lucene upgrade, I get this exception:

org.apache.lucene.index.IndexFormatTooOldException: Format version is not supported (resource BufferedChecksumIndexInput(MMapIndexInput(path="/tmp/lucene/segments_2"))): 3 (needs to be between 4 and 6). This version of Lucene only supports indexes created with release 5.0 and later.

This is expected since Lucene 6 is incompatible with old Lucene 4 indexes, see JENA-1250 for details.

Unless anyone objects I will merge this within the next 2 days.

[rvesse]

Is there a logical place where we could catch that specific exception and provide a more obvious error e.g. Index format is no longer supported, please rebuild the text index with Jena X.Y.Z or higher

If we do that proactively we are likely to get less support questions that if we leave the default error

[osma]

@rvesse Good point! I'll see what I can do. I don't think there are many places where this has to be caught, one or two per module (jena-text and jena-spatial).

[osma]

Added more informative error messages for both jena-text and jena-spatial, as suggested by @rvesse .

[rvesse]

Thanks for adding the more informative error message, the wording is extremely clear and should avoid lots of user confusion