NUTCH-2700 Indexchecker: improve command-line help

[sebastian-nagel]

... and add options -doIndex to pass "checked" document to index writers (the property doIndex is kept to ensure back-ward compatibility):

% bin/nutch indexchecker
Usage:
  IndexingFiltersChecker [OPTIONS] <url>
    Fetch single URL and index it
  IndexingFiltersChecker [OPTIONS] -stdin
    Read URLs to be indexed from stdin
  IndexingFiltersChecker [OPTIONS] -listen <port> [-keepClientCnxOpen]
    Listen on <port> for URLs to be indexed
Options:
  -D<property>=<value>  set/overwrite Nutch/Hadoop properties
                        (a generic Hadoop option to be passed
                         before other command-specific options)
  -normalize            normalize URLs
  -followRedirects      follow redirects when fetching URL
  -dumpText             show the entire plain-text content,
                        not only the first 100 characters
  -doIndex              pass document to configured index writers
                        and let them index it
  -md <key>=<value>     metadata added to CrawlDatum before parsing