index.js: Print a better error if the indexer exits with a signal.
index.js: Print a better error if the indexer exits with a signal.

wfxiang08/livegrep,lekkas/livegrep,wfxiang08/livegrep,lekkas/livegrep,wfxiang08/livegrep,lekkas/livegrep,paulproteus/livegrep,paulproteus/livegrep,paulproteus/livegrep,paulproteus/livegrep,paulproteus/livegrep,wfxiang08/livegrep,lekkas/livegrep,lekkas/livegrep,lekkas/livegrep,wfxiang08/livegrep,wfxiang08/livegrep,paulproteus/livegrep