Prevent OutOfMemory error when POSTing large index dumps to Solr (fixes #21).

Apparently the default Jersey client does not use chunked POST encoding by
default, so the index helper can run out of memory when, on VMs without
lots of RAM available, it tries to send a large index file to Solr. This
change:
 - switches the client to the non-default ApacheHttpClient
 - enables chunked encoding

Tested working with heap size set to -Xmx8m. Additional formatting and
comment cleanups.