test-gpg: start gpg-agent by gpg-connect-agent only if GnuPG v2.1+ detected

Danek Duvall found that gpg-connect-agent of GnuPG 2.0 never starts gpg-agent
daemon. The 2.1 way is documented as "gpg-coonect-agent /bye" [1], which
appears to be different from the 2.0 way [2].

 [1]: https://www.gnupg.org/documentation/manuals/gnupg/Invoking-GPG_002dAGENT.html
 [2]: https://www.gnupg.org/documentation/manuals/gnupg-2.0/Invoking-GPG_002dAGENT.html

Since "gpg-agent --daemon" of GnuPG 2.1 never prints environment variables,
"eval $(gpg-agent --daemon)" would be valid only for GnuPG < 2.1, and we'll
need a different workaround for 2.0. I have no 2.0 environment, I won't
implement it.

tests/hghave.py

@@ -357,6 +357,10 b' def has_gpg():'
 def has_gpg2():
     return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.')
 
+@check("gpg21", "gpg client v2.1+")
+def has_gpg21():
+    return matchoutput('gpg --version 2>&1', br'GnuPG[^0-9]+2\.(?!0)')
+
 @check("unix-permissions", "unix-style permissions")
 def has_unix_permissions():
     d = tempfile.mkdtemp(dir='.', prefix=tempprefix)

tests/test-gpg.t

@@ -12,11 +12,16 b' Test the GPG extension'
   $ GNUPGHOME="$TESTTMP/gpg"; export GNUPGHOME
   $ cp -R "$TESTDIR/gpg" "$GNUPGHOME"
 
-Start gpg-agent, which is required by GnuPG v2, and migrate secret keys
+Start gpg-agent, which is required by GnuPG v2
+
+#if gpg21
+  $ gpg-connect-agent -q --subst /serverpid '/echo ${get serverpid}' /bye \
+  > >> $DAEMON_PIDS
+#endif
+
+and migrate secret keys
 
 #if gpg2
-  $ gpg-connect-agent -q --subst /serverpid '/echo ${get serverpid}' /bye \
-  > >> $DAEMON_PIDS
   $ gpg --no-permission-warning --no-secmem-warning --list-secret-keys \
   > > /dev/null 2>&1
 #endif