[REG] Property Editor: property value not selected when editing property

When editing a property in the property editor, the property's value is not selected, so the user cannot simply start typing in the new value to overwrite the old value.

For line edits, the old text is selected from the first character to the character under the mouse, if any. If no character is under the mouse, no text is selected.

For spin boxes, the old value is selected from the last digit to the digit under the mouse, if any. If no digit is under the mouse, nothing is selected.

This is a regression from Qt 4.4.