fixed #1654 crash of index at buildstops with rlp enabled

git-svn-id: http://sphinxsearch.googlecode.com/svn/trunk@4078 8b96e2b9-35c5-2c16-bc47-5122d61876d4
fixed GROUP_CONCAT result length limit

git-svn-id: http://sphinxsearch.googlecode.com/svn/trunk@4079 8b96e2b9-35c5-2c16-bc47-5122d61876d4