Remove ExpressionLanguage reference for 2.3 version

Remove "Using Expressions for Complex Security Restrictions" section using ExpressionLanguage in 2.3 version.

ExpressionLanguage is a 2.4 feature.
Replace form_enctype(form) with form_start(form).

Since form_enctype(form) is deprecated since 2.3 form_start(form) should be used.
bug #4548 Remove ExpressionLanguage reference for 2.3 version (dangarzon)

This PR was merged into the 2.3 branch.

Discussion
----------

Remove ExpressionLanguage reference for 2.3 version

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3 only
| Fixed tickets |

Remove "Using Expressions for Complex Security Restrictions" section using ExpressionLanguage in 2.3 version.

ExpressionLanguage is a 2.4 feature.

Commits
-------

d1e7334 Remove ExpressionLanguage reference for 2.3 version
Merge branch '2.3' into 2.5

* 2.3:
  Remove ExpressionLanguage reference for 2.3 version
Fixing bad merge
Merge branch '2.3' into 2.5

* 2.3:
  Fixing bad merge
Reverts a commit to 2.3 for 2.4 features. This re-adds them to the 2.5 branch

Revert "Remove ExpressionLanguage reference for 2.3 version"

This reverts commit d1e7334bf94ac82c0f73d549d1b8543f0692c008.

Conflicts:
	best_practices/security.rst
required PHPUnit version in the docs should be updated to 4.2 (or later) since the atLeast() method which is used in some of the tests
bug #4552 required PHPUnit version in the docs should be updated to 4.2 (or later)... (jzawadzki)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4552).

Discussion
----------

required PHPUnit version in the docs should be updated to 4.2 (or later)...

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.6
| Fixed tickets | #4547

Commits
-------

bf8cee6 required PHPUnit version in the docs should be updated to 4.2 (or later) since the atLeast() method which is used in some of the tests
Use the new build env on Travis

faster vms with more ram and cpu, much improved boot times
minor #4561 Use the new build env on Travis (joshk)

This PR was submitted for the master branch but it was merged into the 2.3 branch instead (closes #4561).

Discussion
----------

Use the new build env on Travis

faster vms with more ram and cpu, much improved boot times

Commits
-------

9d582e4 Use the new build env on Travis
bug #4603 Replace form_enctype(form) with form_start(form). (xelaris)

This PR was merged into the 2.3 branch.

Discussion
----------

Replace form_enctype(form) with form_start(form).

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | >=2.3
| Fixed tickets |

Since form_enctype(form) is deprecated since 2.3 form_start(form) should be used.

Commits
-------

21d69eb Replace form_enctype(form) with form_start(form).
Merge branch '2.3' into 2.5

* 2.3:
  Use the new build env on Travis
  required PHPUnit version in the docs should be updated to 4.2 (or later) since the atLeast() method which is used in some of the tests
  Replace form_enctype(form) with form_start(form).
Merge branch '2.5' into 2.6

* 2.5:
  Use the new build env on Travis
  required PHPUnit version in the docs should be updated to 4.2 (or later) since the atLeast() method which is used in some of the tests
  Reverts a commit to 2.3 for 2.4 features. This re-adds them to the 2.5 branch
  Fixing bad merge
  Replace form_enctype(form) with form_start(form).
  Remove ExpressionLanguage reference for 2.3 version