bug symfony#25751 [FrameworkBundle] Add the missing enabled session attribute (sroze)

This PR was merged into the 2.7 branch.

Discussion
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[FrameworkBundle] Add the missing `enabled` session attribute

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ø
| License       | MIT
| Doc PR        | ø

Add a missing `enabled` field in framework's `session` configuration.

Commits
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a314931 Add the missing `enabled` session attribute

Author: fabpot

src/Symfony/Bundle/FrameworkBundle/Resources/config/schema/symfony-1.0.xsd

@@ -104,6 +104,7 @@
     </xsd:complexType>
 
     <xsd:complexType name="session">
+        <xsd:attribute name="enabled" type="xsd:boolean" />
         <xsd:attribute name="storage-id" type="xsd:string" />
         <xsd:attribute name="handler-id" type="xsd:string" />
         <xsd:attribute name="name" type="xsd:string" />