Pinentry and passphrase file button

[Ben Kibbey]

Does anyone object to adding a button to the pinentry dialogs to fill
the passphrase text field with the contents of a file? The passphrase
file may contain control characters so maybe adding a checkbox to toggle
the text field, a new filename text field and file button would be
better.

Also, since the passphrase file may contain control characters (nil
included), many functions in gpg-agent would need to be passed the
length of the passphrase rather than potentially truncating it. Or maybe
only issue a warning in pinentry if the passphrase would be truncated?

-- 
Ben Kibbey