kdenlivedoc.cpp:

kdenlivedoc.cpp:
- revert document loading logic, so that errors are handled first
- validate the document instead of simply upgrading it
- share the code for the creation of a new project
- set the correct document version in saved files

documentvalidator.(h|cpp):
- replace documentconvert.(h|cpp)
- the upgrade function now works with incremental changes
- start a validation function to check that the document can really be handled by kdenlive

svn path=/trunk/kdenlive/; revision=3513