take lock in checkLogFile and calcLogFile

take lock in checkLogFile and calcLogFile

move: Fix openFile crash with -J

This does make them a bit slower, although usually the log file is not
very big, so even when it's being rewritten, they will not block for
long taking the lock. Still, little slowdowns may add up when moving a lot
file files.

A less expensive fix would be to use something lower level than openFile
that does not check if the file is already open for write by another
thread. But GHC does not seem to provide anything convenient; even mkFD
checks for a writing thread.

fullLines is no longer necessary since these functions no longer will
read the file while it's being written.

Sponsored-by: Dartmouth College's DANDI project