Replace form_enctype(form) with form_start(form).

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