Dropped last_id on XML

provide a good default value for migrateToHBTree()'s new_generate_id_method argument, suggested by Tatuya.

Also, declare ERP5Site.getVersionPriorityNameList() as protected rather than
private for views.

This is similar to portal skins priority, except that versions and priorities
are defined on ERP5Site (as 'VERSION | PRIORITY' where PRIORITY is a float) as
there is not one Folder for each version in contrary to portal skins.

On the Business Template itself, versions and priorities can be defined like
'VERSION | PRIORITY' or simply 'VERSION' (where PRIORITY is assumed to be
0.0). Upon installation, it will be merged into ERP5Site property in
descending order (by priority first and then by version for versions with the
same priority).

considered as a Document for DMS for example.

When load() was called in checkConsistency where namespace_dict was not given
and thus equal to the default function parameter value, exec would set the
function namespace_dict parameter, thus the next call would have
namespace_dict already set when it was given.

This fixes testInvalidSourceCode when being ran for TestZodbExtensionComponent
and TestZodbDocumentComponent in the same runUnitTest.

Only consider .py and .xml files when importing BusinessTemplate files in FilesystemToZodbTemplateItem.

This fixes tests failures with ``AttributeError: 'str' object has no attribute
'text_content''' due to .pyc files.

Fix hasErrorMessageList() of ZODB Component as error_message (component_validation_workflow variable) is always set.

Modules to be handled by the Component import hook must have already been
filtered properly in find_module().

Add ZODB Document BusinessTemplate tests as expected failure for Constraint and Test (not implemented yet).

This fixes filesystem Document-related tests in testBusinessTemplate.

Otherwise, following ZODB Document tests will fail because of the ZODB
Document created but not removed in that test.