compilation: fix std::find() == 0 misuse

cppcheck correctly warns about the old code as less efficient (looks
at entire string instead of just the start). Using boost::starts_with
is less obscure and avoids the warning.

src/dbus/server/session.cpp

@@ -306,7 +306,7 @@ void Session::setNamedConfig(const std::string &configName,
         /** generate new sources in the config map */
         for (ReadOperations::Config_t::const_iterator it = config.begin(); it != config.end(); ++it) {
             string sourceName = it->first;
-            if(sourceName.find("source/") == 0) {
+            if (boost::starts_with(sourceName, "source/")) {
                 sourceName = sourceName.substr(7); ///> 7 is the length of "source/"
                 from->getSyncSourceNodes(sourceName);
             }

src/syncevo/Cmdline.cpp

@@ -198,7 +198,7 @@ bool Cmdline::parse(vector<string> &parsed)
             m_template = m_argv[opt];
             m_configure = true;
             string temp = boost::trim_copy (m_template);
-            if (temp.find ("?") == 0){
+            if (boost::starts_with(temp, "?")) {
                 m_printTemplates = true;
                 m_dontrun = true;
                 m_template = temp.substr (1);

src/syncevo/SyncContext.cpp

@@ -1691,7 +1691,7 @@ boost::shared_ptr<TransportAgent> SyncContext::createTransportAgent(void *gmainl
         InitializeTransport(agent, timeout);
         return agent;
 #endif
-    } else if (url.find("obex-bt://") ==0) {
+    } else if (boost::starts_with(url, "obex-bt://")) {
 #ifdef ENABLE_BLUETOOTH
         std::string btUrl = url.substr (strlen ("obex-bt://"), std::string::npos);
         boost::shared_ptr<ObexTransportAgent> agent(new ObexTransportAgent(ObexTransportAgent::OBEX_BLUETOOTH,