xpath.py: Removed unnecessary copy.deepcopy()'s and instead changed set_value() and set_id() to make copies of any elements they change. This should result in up to a 17% speed increase in the import, because deepcopy() was taking a lot of time. Added documentation to set_value() and set_id() that caller must make a shallow copy of the path to prevent modifications from propagating to other copies of the path. (Previously, a deep copy was needed, but there was no comment specifying this.)
xpath.py: Removed unnecessary copy.deepcopy()'s and instead changed set_value() and set_id() to make copies of any elements they change. This should result in up to a 17% speed increase in the import, because deepcopy() was taking a lot of time. Added documentation to set_value() and set_id() that caller must make a shallow copy of the path to prevent modifications from propagating to other copies of the path. (Previously, a deep copy was needed, but there was no comment specifying this.)