[2.6] Remove possible call_user_func()
[2.3] Remove possible call_user_func()
[2.5] Remove possible call_user_func()
removed unneeded check

It is already checked in the `isEnabled()` method of the parent
`ServerCommand` class if the current PHP build is HHVM and the
`server:start` command is never enabled then. Thus, it's not needed
to check for HHVM on every command execution.

This was pointed out by @stof in #12489 for the `server:run` command.
updated CHANGELOG for 2.6.0
updated VERSION for 2.6.0
Improved error message
bumped Symfony version to 2.6.1
minor #12552 [FrameworkBundle] removed unneeded check (xabbuh)

This PR was merged into the 2.6 branch.

Discussion
----------

[FrameworkBundle] removed unneeded check

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

It is already checked in the `isEnabled()` method of the parent
`ServerCommand` class if the current PHP build is HHVM and the
`server:start` command is never enabled then. Thus, it's not needed
to check for HHVM on every command execution.

This was pointed out by @stof in #12489 for the `server:run` command.

Commits
-------

ce2adfa removed unneeded check
Fixed a docblock
Fixed typos
add deprecation log (#12618)
Fix incorrect spanish translation
minor #12644 Fix incorrect spanish translation (alfonso)

This PR was submitted for the 2.5 branch but it was merged into the 2.3 branch instead (closes #12644).

Discussion
----------

Fix incorrect spanish translation

SymfonyCon Madrid 2014 Hackday

Commits
-------

28b07ba Fix incorrect spanish translation
issue 12664
minor #12638 [Hackday][2.3] Fixed typos (pborreli)

This PR was merged into the 2.3 branch.

Discussion
----------

[Hackday][2.3] Fixed typos

Commits
-------

7a67e8c Fixed typos
Add deprecation message for Process
[Stopwatch] added __toString on StopwatchEvent
minor #12632 Fixed a docblock (GrahamCampbell)

This PR was merged into the 2.6 branch.

Discussion
----------

Fixed a docblock

Commits
-------

e130a29 Fixed a docblock
define constant only if it wasn't defined before