Fixed bugs:
- Fix potential deadlock
- Fix potential crash
Improvements:
- Allow building with -DCRYFS_UPDATE_CHECKS=off, which will create an executable with disabled update checks (the alternative to disable them in the environment also still works).
- Automatically disable update checks when running in noninteractive mode.
- More detailed error reporting if key derivation fails
Compatibility:
- Compatible with libcurl version >= 7.50.0, and <= 7.21.6 (tested down to 7.19.0)
- Compatible with Crypto++ 5.6.4
- Compatible with compilers running under hardening-wrapper