lock rt-fulltext-indexer so only one instance can be run at the same time

multiple instances eat more cpu and may also break stuff.

see also #17423
add --quiet option to make fulltext-indexer more convenient in cron env

so we can exit processes quietly and normally.
Minor wordsmithing, and copy the paragraph to Oracle as well
Merge branch '4.0/lock-fulltext-indexer' into 4.0-trunk