mongoimport: trap SIGUSR1 to flush buffer
If mongoimport is run in the background as a daemon, the user doesn't have many good ways to manually flush the buffer from a scripting standpoint. By default mongoimport flushed data every 1000 documents.
This feature as already requested at https://jira.mongodb.org/browse/TOOLS-2773 but was closed. I still have the hope that it will be introduced somewhere in future release.