Adding details about the changes to the PdoSessionHandler in 2.6
Updating statements, now that we're not overriding the names
Fixes thanks to comments and a new note about the LegacyPdoSessionHandler
feature #4609 Adding details about the changes to the PdoSessionHandler in 2.6 (weaverryan)

This PR was merged into the 2.6 branch.

Discussion
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Adding details about the changes to the PdoSessionHandler in 2.6

Hi guys!

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | yes symfony/symfony#12833
| Applies to    | 2.6+
| Fixed tickets | n/a

This follows #4557.

This adds more details about the table schema changes to the PdoSessionHandler in 2.6. I also made some improvements (not showing all the extra configuration by default), which I'll backport to 2.3 after this is accepted.

Thanks!

Commits
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1e34823 Fixes thanks to comments and a new note about the LegacyPdoSessionHandler
2f974bb Updating statements, now that we're not overriding the names
fd8b552 Adding details about the changes to the PdoSessionHandler in 2.6