R1:6219d30f6b0b

Recommend dumping database backups with "--compress --output X" instead of "| gzip > X"

Summary:
Fixes T13304. Shell pipes and redirects do not have robust behavior when errors occur. We provide "--compress" and "--output" flags as robust alternatives, but do not currently recommend their use.

- Recommend their use, since their error handling behavior is more robust in the face of issues like full disks.
- If "--compress" is provided but won't work because the "zlib" extension is missing, raise an…