reduce the number of open file descriptors

[tstack]

A file descriptor is kept open for every file that is opened, so we are bound to hit a limit when trying to open a lot of files.

[FaffeF]

Not only that, but a lot of "... No file descriptors available" flash by, and then lnav crashes with ==== Guru meditation ====. Very sad. Was trying to open ~6000 daily rotated logs from a lot of hosts.