…ways return the correct binary

…orrect binary

This PR was submitted for the master branch but it was merged into the 2.2 branch instead (closes #8456).

Discussion
----------

[Process] Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary

Since `PHP_BINARY` is the very first approach considered, there is no way to use a workaround like setting the `PHP_PATH`.

Checking `PHP_PATH` could potentially be put before checking `PHP_BINARY`: that would avoid an extra function call (and system call), at the price of a small BC_BREAK, but I think it's better in this case to have a solution that doesn't force people to set the `PHP_PATH` environment variable.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #8455
| License       | MIT
| Doc PR        | none

Commits
-------

35a2fe4 [Process] Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary

* 2.2:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class

Conflicts:
	src/Symfony/Component/Validator/Tests/Constraints/CollectionTest.php
	src/Symfony/Component/Validator/Tests/GraphWalkerTest.php

* 2.3:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed #8455: PhpExecutableFinder::find() does not always return the correct binary
  Added missing files .gitignore
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class
  [Form] Fix of "PATCH'ed forms are never valid"

* 2.3:
  [Validator] fixed ConstraintViolation:: incorrect when nested
  handle Optional and Required constraints from XML or YAML sources correctly
  added missing comments to WebTestCase
  Fixed symfony#8455: PhpExecutableFinder::find() does not always return the correct binary
  Added missing files .gitignore
  [DependencyInjection] Fix Container::camelize to convert beginning and ending chars
  [Validator] Fixed groups argument misplace for validateValue method from validator class
  [Form] Fix of "PATCH'ed forms are never valid"