[[ Bug 13034 ]] Documentation added about the relation between 'return' ...

...and 'the result'.

As usual the updates are not seeable, since the doc file format has totally changed, here are the changes:
- adding to function's and on's descriptions:  "As the <function tag="result">result</function> is a global property, if you do not explicitly <control_st tag="return">return</control_st> a value, then <function tag="result">the result</function> will no change, but reflect the last engine command, engine function or command or function handler that did return a value.
- adding to return's summary: "Sets the result to the value as well"
- adding to return's description: "<note>As well as the <b>return</b> <glossary tag="control structure">control structure</glossary> returns the value to the caller, it sets <function tag="result">the result</function> to the value</note>"
- changing result's summary to: "Is a global property returning the last value returned by return from a handler, from an engine function, or from an engine command which sets the result."
- changing first sentence of result's description to: "Use the <b>result</b> <control_st tag="function">function</control_st> to check whether the last <glossary tag="command">command</glossary> <glossary tag="execute">executed</glossary> encountered an <glossary tag="error">error</glossary>, or get the last value returned by the control structure <control_st tag="return">return</control_st>"