Fix button box in options dialog not working (fix #11960)

QgsOptionsDialogBase was incorrectly finding the projection
selector's buttonBox widget and attaching the connections
to that widget, rather than the dialog's widget.

Rename projection selector's button box to avoid this conflict.

Author: nyalldawson

python/gui/qgsgenericprojectionselector.sip

@@ -31,7 +31,7 @@ class QgsGenericProjectionSelector : QDialog //, private Ui::QgsGenericProjectio
     void setSelectedCrsId( long theID );
     void setSelectedAuthId( QString authId );
 
-    void on_buttonBox_helpRequested();
+    void on_mButtonBox_helpRequested();
 
     /**
      * \brief filters this dialog by the given CRSs

src/gui/qgsgenericprojectionselector.h

@@ -69,7 +69,7 @@ class GUI_EXPORT QgsGenericProjectionSelector : public QDialog, private Ui::QgsG
     void setSelectedCrsId( long theID );
     void setSelectedAuthId( QString authId );
 
-    void on_buttonBox_helpRequested() { QgsContextHelp::run( metaObject()->className() ); }
+    void on_mButtonBox_helpRequested() { QgsContextHelp::run( metaObject()->className() ); }
 
     /**
      * \brief filters this dialog by the given CRSs

src/ui/qgsgenericprojectionselectorbase.ui

@@ -57,7 +57,7 @@
     <widget class="QgsProjectionSelector" name="projectionSelector" native="true"/>
    </item>
    <item row="2" column="0">
-    <widget class="QDialogButtonBox" name="buttonBox">
+    <widget class="QDialogButtonBox" name="mButtonBox">
      <property name="standardButtons">
       <set>QDialogButtonBox::Cancel|QDialogButtonBox::Help|QDialogButtonBox::Ok</set>
      </property>
@@ -80,7 +80,7 @@
  <resources/>
  <connections>
   <connection>
-   <sender>buttonBox</sender>
+   <sender>mButtonBox</sender>
    <signal>accepted()</signal>
    <receiver>QgsGenericProjectionSelectorBase</receiver>
    <slot>accept()</slot>
@@ -96,7 +96,7 @@
    </hints>
   </connection>
   <connection>
-   <sender>buttonBox</sender>
+   <sender>mButtonBox</sender>
    <signal>rejected()</signal>
    <receiver>QgsGenericProjectionSelectorBase</receiver>
    <slot>reject()</slot>