Add function to export public keys.

Expects a fingerprint to export a single public key in armor mode.

GpgMEWorker.cpp

@@ -280,3 +280,18 @@ const Error GpgMEWorker::ExportPrivateKey(const char * pattern, string& buffer,
     return e;
 }
 #endif
+
+const Error GpgMEWorker::ExportPublicKey(const char* pattern, string& buffer)
+{
+    GpgME::Data kData;
+    Context * ctx = Context::createForProtocol(Protocol::OpenPGP);
+    ctx->setArmor(true);
+    uint flags = Context::ExportDefault;
+
+    Error e = ctx->exportPublicKeys(pattern, kData, flags);
+    buffer = kData.toString();
+
+    delete ctx;
+
+    return e;
+}

GpgMEWorker.h

@@ -148,7 +148,13 @@ public:
     const Error ExportPrivateKey(const char * pattern, string& buffer,
                                  const string& passphrase = "");
 #endif
-
+    /**
+     * Export a public key.
+     * @param pattern : a key fingerprint
+     * @param buffer : returns data in armor mode
+     * @return 
+     */
+    const Error ExportPublicKey(const char * pattern, string& buffer);
 private:
     Context * m_ctx;
     // GPG will fetch a password here.