Use explict form of specifing $REAL_USER_ID and $EFFECTIVE_USER_ID

Dovecot can be setup to run as a virtual user, for example 'vmail'.
Sieve scripts are then run with the UID of root but the EUID of
the vmail user. GnuPG will not run if the EUID does not match the
UID as a measure to prevent the system letting it keep root privs.
http://lists.gnupg.org/pipermail/gnupg-users/2006-August/029109.html

gpgit

@@ -59,7 +59,7 @@ use MIME::Parser;
   $ENV{HOME} = (getpwuid($>))[7];
 
 ## Set the UID to match the EUID to prevent errors from GnuPG.
-  $< = $>;
+  $REAL_USER_ID = $EFFECTIVE_USER_ID;
 
 ## Object for GPG encryption
   my $gpg = new Mail::GnuPG();