Improve error messages when opening a bad file; instead of saying that the file couldn't be found say also that the tree that podio looks for couldn't be read
ENDRELEASENOTES
A bit more precise since the current error messages will always say that the file couldn't be found when it's possible that the file exists but it's a bad file.
BEGINRELEASENOTES
ENDRELEASENOTES
A bit more precise since the current error messages will always say that the file couldn't be found when it's possible that the file exists but it's a bad file.