Index usage for "not equals" conditions

Queries with "not equals" conditions don't currently use an index. Example:

/jcr:root/content//*[@contentType != 'container']

Such conditions should result in a "not null" property restrictions (so that property indexes can be used if available, and if there are only few entries for this property).

Also, "not equal" need to be used and supported in the filter. Currently, in FilterImpl, this is not supported and used, and would throw a IllegalArgumentException if used. This is for indexes that natively support this feature (such as Apache Lucene and Solr).

Also, this needs to be supported in the Lucene and Solr index.