Fix resolveImportLinks error (attempt 1)

Release notes

Fixed an error with resolveImportLinks when a TQFolder is split but kept in memory

Details

When splitting a TQFolder (e.g. while writing it to a file with a split level defined at its depth), the isFullyResolved member variable is not correctly set back to false. Therefore, if resolveImportLinks is later called on the same TQFolder, the import links aren't actually resolved since isFullyResolved is still set to true.

This issue only arises when the TQFolder is kept in memory, since isFullyResolved isn't written to disk with the ROOT streamer. When the TQFolder is read back from disk, isFullyResolved is correctly set to false such that resolveImportLinks will actually resolve the import links.

The handling of isFullyResolved is also updated in a couple of other locations as well.

Attempts to address #37 (closed)