S3 has memory leaks

## with encryption

One only occurs with encryption. It was was fixed for bup, but
not yet for S3, in 5985acdfad8a6791f0b2fc54a1e116cee9c12479.
(The fix I used for bup doesn't seem to work with S3.)

## always

Copying the file back from S3 causes a slow memory increase toward 119 mb.

The author of hS3 is aware of the problem, and working on it.

## fixed

memory leak while uploading content to S3