Added testcase for prefix getter on JakartaRegexpCapabilities. During LUCENE-2072 dev the prefix method did always return null due to a bug in jakarta-regexp-1.5. This testcase mainly prevents other from simply upgrading as long as this bug has not been fixed.
lucene/java/trunk/contrib/regex/src/test/org/apache/lucene/search/regex/TestJakartaRegexpCapabilities.java