[Lazarus] New XML format for project info files

[Werner Pamler]

Am 15.03.2019 um 17:39 schrieb Juha Manninen via lazarus:
> Yes, there is option :
>    Maximize compatibility of project files (LPI and LPS)
> in Project Options -> Miscellaneous.
> I did not test the option much myself. I guess it will get tested now
> by you and many others. It is a typical use case after all.

I think we have a big mess now. This option must be ON at least until 
the release of the next version. The way it is now the current release 
version cannot read any project modified by trunk.

And what happens when the next release appears? We will have the same 
situation. This way the new format can never be introduced without 
breaking the current release version unless the information is written 
in some kind of duplicate way: The old version always reads the old 
nodes if new nodes are not available, or the new nodes otherwise, the 
new version writes both old and new nodes when the compatibility option 
is ON. Later, a few versions in the future, when all old nodes have been 
replaced by new nodes we can switch the default of compatibility option 
to OFF.