prompt for pin before operations

[Abel Luck]

Hi,

A standard --sign --encrypt on a large file can take some time,
especially on an ARM device like most Android phones.

Currently, GnuPG is encrypting the data and then invoking pinentry for
the sign operation. This is a usability problem on Android, as the user
can background the long-running encrypt operation and do other things,
and the pin entry prompt sort of gets lost in the background.

Is it possible to force GnuPG to prompt for the pin before invoking a
potentially long-running operation?

This is of course gnupg from master.

~abel