Upgrade persistence of user models in idea plugin projects
Fix MPSModelVirtualFile.getParent(): work correctly both for single-file and multi-file. Return either file or directory correspondingly.
 Previous fix (FileDataSource -> FileSystemBaseDataSource) was broken.
MPSPsiModel and RootNode
Fix: root nodes not shown in per-root model in plugin
Fixing exception related to PsiBinaryFile due to usage of LightVirtualFile. Exception happened during any find usages