Fix ignored ids for belongsToMany relations

Fix ids ignored by marshaller for belongsToMany relations.
fix FileEngine, divergent behavior when debug is off or on
Added comment to $tableParameters array
Added tests for MySQL table comment feature
Now the tableParameters array gets escaped through values(), too
Merge pull request #4897 from ravage84/2.6-mysql-table-comments

2.6 Add Support for MySQL Table Comments
Handle query string arguments in digest auth data.

Handle &, ? in digest auth data uri.

Refs #4908
Documentation correction
Merge pull request #4921 from dmromanov/patch-1

Documentation correction
Removed the code that was never being executed
Merge pull request #4930 from jrbasso/2.6-not-executed

Removed the code that was never being executed
Simplified way to add new prefixes to the router
Replaced for loops by foreach
Merge pull request #4940 from jrbasso/2.6-router-optimization-2

Replaced for loops by foreach
Update .gitattributes

PDF is a common file that should not be modified.
Removing unrelated parameter in comment

That parameter doesn't exists in display() function (in fact is not a parameter) and is breaking the [CakePHP code standards]:https://github.com/cakephp/cakephp-codesniffer
Merge pull request #4947 from agarzon/patch-2

Removing unrelated parameter in comment
Fix views overwrite warning text
Merge pull request #4950 from bcrowe/fix-viewtask

Fix views overwrite warning text
Merge pull request #4944 from agarzon/patch-1

Update .gitattributes