Fixed assumption that `_i_table` only exists when `table` is indexed.
Fixed assumption that `_i_table` only exists when `table` is indexed.

This assumption is wrong when moving or removing a table, and may lead to stale
group indexes.  So the existence of the index group is checked instead of
whether the table is indexed.  The check is performed by a `try` statement to
avoid `File.__contains__()` and then `File._getNode()`, which are way slower.


git-svn-id: 92c705c98a17f0f7623a131b3c42ed50fcde59b4@2281 1b98710c-d8ec-0310-ae81-f5f2bcd8cb94

tp199911/PyTables,dotsdl/PyTables,rdhyee/PyTables,PyTables/PyTables,jack-pappas/PyTables,tp199911/PyTables,PyTables/PyTables,cpcloud/PyTables,avalentino/PyTables,jack-pappas/PyTables,tp199911/PyTables,andreabedini/PyTables,mohamed-ali/PyTables,rabernat/PyTables,jennolsen84/PyTables,andreabedini/PyTables,gdementen/PyTables,rabernat/PyTables,jennolsen84/PyTables,dotsdl/PyTables,dotsdl/PyTables,rdhyee/PyTables,joonro/PyTables,gdementen/PyTables,avalentino/PyTables,dotsdl/PyTables,mohamed-ali/PyTables,rabernat/PyTables,joonro/PyTables,FrancescAlted/PyTables,cpcloud/PyTables,jack-pappas/PyTables,jack-pappas/PyTables,gdementen/PyTables,jennolsen84/PyTables,jennolsen84/PyTables,joonro/PyTables,FrancescAlted/PyTables,cpcloud/PyTables,rdhyee/PyTables,andreabedini/PyTables,gdementen/PyTables,andreabedini/PyTables,tp199911/PyTables,rdhyee/PyTables,FrancescAlted/PyTables,joonro/PyTables,cpcloud/PyTables,jack-pappas/PyTables,avalentino/PyTables,mohamed-ali/PyTables,rabernat/PyTables,PyTables/PyTables,mohamed-ali/PyTables