Configuring for use of gpg-agent by default for Gutsy

[Scott Kitterman]

One of the goals for KDE in Gutsy is to support S/MIME encryption/signing by 
default in kmail/kontact:

https://wiki.kubuntu.org/KubuntuGutsyPlan

One of the requirements for meeting this goal is to set "use-agent" in the 
~/.gnupg/gpg.conf of the user.  I've done some investigation and it seems to 
me that there is not a significant risk associated with just doing this 
generally.  

If the string is set and gnupg-agent is not installed, pgp signing/encryption 
still works.  All that happens is gnupg prints a warning that no running 
agent can be found, but it happily asks for a passphrase using the normal CLI 
interface.

The only issue I've found with using gpg-agent with an appropriate pinentry 
program is a problem in debuild with the way that it destroyed the local 
environment and then called debsign.  This was fixed in the last devscripts 
upload by Steve Kowalik (seahorse-agent will also now work with debuild).

From a KDE perspective, one side benifit of enabling agent out of the box is 
that gpg signing/encryption will also work as soon as kmail has been set up 
for it (i.e. set up the keys to use for signing/encryption).

There are no doubt hacks we could come up with to set "use-agent" when 
kmail/kontact is installed, but it seems to me that setting it by default is 
the cleanest approach with no real downside risk that I've been able to 
identify.

Scott K