Update pdo_session_storage.rst

Changes after the 2.6.0 release keeping the names of the values as they where.
feature #4557 Update pdo_session_storage.rst (spbentz)

This PR was submitted for the master branch but it was merged into the 2.6 branch instead (closes #4557).

Discussion
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Update pdo_session_storage.rst

Changes after the 2.6.0 release keeping the names of the values as they where.

Commits
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3e51551 Update pdo_session_storage.rst