compilation: fix boost::shared_ptr->bool issue under C++14

The implicit conversion of boost::shared_ptr->bool is no
longer supported when compiling as C++14 (the default under
gcc 6). We have to cast explicitly.

Fixes errors like this:

Logging.h:258:41: error: cannot convert 'const boost::shared_ptr<SyncEvo::Logger>' to 'bool' in return
         operator bool () const { return m_logger; }

src/dbus/server/session.h

@@ -425,7 +425,7 @@ public:
     void setServerAlerted(bool serverAlerted) { m_serverAlerted = serverAlerted; }
 
     void initServer(SharedBuffer data, const std::string &messageType);
-    void setStubConnection(const boost::shared_ptr<Connection> c) { m_connection = c; m_useConnection = c; }
+    void setStubConnection(const boost::shared_ptr<Connection> c) { m_connection = c; m_useConnection = static_cast<bool>(c); }
     boost::weak_ptr<Connection> getStubConnection() { return m_connection; }
     bool useStubConnection() { return m_useConnection; }
 

src/syncevo/Logging.h

@@ -255,7 +255,7 @@ class Logger
         Handle &operator = (const Handle &other) throw ();
         ~Handle() throw ();
 
-        operator bool () const { return m_logger; }
+        operator bool () const { return static_cast<bool>(m_logger); }
         bool operator == (Logger *logger) const { return m_logger.get() == logger; }
         Logger *get() const { return m_logger.get(); }
 

src/syncevo/StringDataBlob.h

@@ -53,7 +53,7 @@ class StringDataBlob : public DataBlob
 
     virtual boost::shared_ptr<std::string> getData() { return m_data; }
     virtual std::string getName() const { return m_name; }
-    virtual bool exists() const { return m_data; }
+    virtual bool exists() const { return static_cast<bool>(m_data); }
     virtual bool isReadonly() const { return m_readonly; }
 };