no-use-agent is obsolete for GPG2

(cherry picked from commit 19fd35c7232e42a4112c8f18686df1c0407c2d0d)
Signed-off-by: Isis Lovecruft <isis@leap.se>

 * FIXES #96.
 * CLOSES #96.
 * CLOSES #46.

gnupg/_meta.py

@@ -538,7 +538,7 @@ class GPGBase(object):
         if passphrase: cmd.append('--batch --passphrase-fd 0')
 
         if self.use_agent: cmd.append('--use-agent')
-        else: cmd.append('--no-use-agent')
+        elif self.use_agent==False: cmd.append('--no-use-agent') # obsolete for GPG 2.0
 
         # The arguments for debugging and verbosity should be placed into the
         # cmd list before the options/args in order to resolve Issue #76:

gnupg/gnupg.py

@@ -161,6 +161,9 @@ class GPG(GPGBase):
         # fatal error (at least it does with GnuPG>=2.0.0):
         self.create_trustdb()
 
+            # --no-use-agent is obsolete
+            if not self.use_agent: self.use_agent = None 
+
     @functools.wraps(_trust._create_trustdb)
     def create_trustdb(self):
         if self.is_gpg2():