QT linguist expands XML entities in XLIFF ids

If an XLIFF segment's id contains XML entities, they are resolved and saved in plain text.

Eg :

A file containing this

<trans-unit xml:space="preserve" id="foo &quot;bar&quot; baz" approved="yes">
  <source>XXX</source>
  <target state="translated">YYY</target>
</trans-unit>

will be saved like this

<trans-unit xml:space="preserve" id="foo "bar" baz" approved="yes">
  <source>XXX</source>
  <target state="translated">YYY</target>
</trans-unit>

After that, even QT Linguist will be unable to read the file.