Support direct file input

[sebbASF]

At present the commands such as key import and file verify rely on copying the data to a temporary file.
This seems very inefficient.
Surely the file name could just be passed to the gpg application?

[vsajip]

Possibly, but in general the way it works now is "fast enough" for most applications. At least, no one has brought any performance problems to my attention.

[sebbASF]

It's not just speed / unnecessary resource usage.
It also relies on the client code to open/read the file with the correct options.
That should not be the concern of the client.

[vsajip]

It may require new APIs to support paths in the API while preserving backward-compatibility. What would the API signatures be for the affected APIs, in your view?

[sebbASF]

I think the APIs could remain the same in most cases.
If it is a string, process it as a file name. Possibly check for file existence.
Otherwise assume it is a file-type object.

This should work for verify_file, encrypt_file, decrypt_file, get_recipients_file.
import_keys would need a corresponding import_keys_file.
[scan_keys already expects a filename]

[vsajip]

Should be fixed in 334b90d.