SERVER-4345 Add support processing fifo files in mongorestore

Example : `./mongorestore -d test -c foo_dupl <(mongodump -d test -c foo -out - 2>/dev/null | tail -n+2)`
Example (after pull #204) : `./mongorestore -d test -c foo_dupl <(mongodump -d test -c foo -out - 2>/dev/null)`

This closes #205

Signed-off-by: Benety Goh <benety@mongodb.com>
SERVER-4345 mongorestore will read from stdin when filename is "-"
            check eof only on fifo files. restored original logic of checking bytes read against file length.
            mongorestore requires both --db and --collection when using stdin/fifo