Help: Clarify/add docs for initializing AUTO..._OPTIONS properties

Help/prop_tgt/AUTOMOC_MOC_OPTIONS.rst

@@ -9,7 +9,9 @@ options which will be used when ``moc`` is executed during the build, i.e.
 it is equivalent to the optional ``OPTIONS`` argument of the
 :module:`qt4_wrap_cpp() <FindQt4>` macro.
 
-By default it is empty.
+This property is initialized by the value of the
+:variable:`CMAKE_AUTOMOC_MOC_OPTIONS` variable if it is set when a target
+is created, or an empty string otherwise.
 
 See the :manual:`cmake-qt(7)` manual for more information on using CMake
 with Qt.

Help/prop_tgt/AUTORCC_OPTIONS.rst

@@ -8,11 +8,9 @@ when ``rcc`` is executed during the build via :prop_tgt:`AUTORCC`,
 i.e. it is equivalent to the optional ``OPTIONS`` argument of the
 :module:`qt4_add_resources() <FindQt4>` macro.
 
-By default it is empty.
-
 This property is initialized by the value of the
 :variable:`CMAKE_AUTORCC_OPTIONS` variable if it is set when a target is
-created.
+created, or an empty string otherwise.
 
 The options set on the target may be overridden by :prop_sf:`AUTORCC_OPTIONS`
 set on the ``.qrc`` source file.

Help/prop_tgt/AUTOUIC_OPTIONS.rst

@@ -8,11 +8,9 @@ This property holds additional command line options which will be used when
 equivalent to the optional ``OPTIONS`` argument of the
 :module:`qt4_wrap_ui() <FindQt4>` macro.
 
-By default it is empty.
-
 This property is initialized by the value of the
 :variable:`CMAKE_AUTOUIC_OPTIONS` variable if it is set when a target is
-created.
+created, or an empty string otherwise.
 
 The options set on the target may be overridden by :prop_sf:`AUTOUIC_OPTIONS`
 set on the ``.ui`` source file.