Improve the description of the 'same as' test

This description of the 'same as' test is based on the description in the docblock for Twig_Node_Expression_Test_Sameas. It reads better than the one currently used in the docs.
minor #1406 Improve the description of the 'same as' test (adamelso)

This PR was merged into the 1.15-dev branch.

Discussion
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Improve the description of the 'same as' test

This description of the `same as` test is based on the description in the docblock for `Twig_Node_Expression_Test_Sameas`. It reads better than the one currently used in the docs.

Commits
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e4b7db1 Improve the description of the 'same as' test