In analogy to the xml-parser add a device-table to git's parser-state.
Currently this is unused. In upcoming commits the git parser will
then be changed to add device nodes in this table instead of the
global device table. The long-term goal being to detach the
parsers from global state and to make dive-import fully undoable.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
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