Make DirManager::MoveToNewProjectDirectory(), DirManager::CopyToNewProjectDirectory(), and several BuildFromXML() methods check the result of AssignFile() and do something appropriate about it on failure, rather than ignoring it. Also made AssignFile() check whether the assigned name is well-formed, so it doesn't always return TRUE when disckcheck is FALSE.
Briefer and more correct checks for uninitialized wxFileName objects.
Several "//ANSWER-ME" comments about file ops and commented-out cruft to probably remove.
Clarify some logic and readability.
better handling of error conditions in all BuildFromXML methods, per comment:
// BuildFromXML methods should always return a BlockFile, not NULL,
// even if the result is flawed (e.g., refers to nonexistent file),
// as testing will be done in DirManager::ProjectFSCK().
