[HttpFoundation] Optimize ServerBag::getHeaders()

isset() vs in_array makes it take half the time (1ms/req here)
substr() does not have to scan the whole string so it's a wee bit faster
[HttpFoundation] Avoid a few unnecessary str_replace() calls
[HttpKernel] Avoid updating the context if the request did not change

Due to the BC $this->setRequest() call in the onKernelRequest method, the
request is set twice every time in Symfony, and RequestContext::fromRequest
takes 1ms to run here so if we can skip one call it is a win.
[DependencyInjection] Add a method map to avoid computing method names from service names
[Security] fixed wrong merge (refs #4776)
[Form] Added radio button for empty value to expanded single-choice fields
merged branch fabpot/require-previous-session (PR #7938)

This PR was merged into the master branch.

Discussion
----------

[Security] fixed wrong merge (refs #4776)

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

This fixes a bad conflict resolution when #4776 was merged.

Commits
-------

1856df3 [Security] fixed wrong merge (refs #4776)
fixed DocBlock
merged branch bschussek/issue3154 (PR #7939)

This PR was merged into the master branch.

Discussion
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[Form] Added radio button for empty value to expanded single-choice fields

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #3154
| License       | MIT
| Doc PR        | symfony/symfony-docs#2605

Commits
-------

7933971 [Form] Added radio button for empty value to expanded single-choice fields
fixed CS
merged branch Aitboudad/patch-3 (PR #7941)

This PR was merged into the master branch.

Discussion
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fixed DocBlock

Commits
-------

aecc495 fixed DocBlock
merged branch Seldaek/optim (PR #7931)

This PR was merged into the master branch.

Discussion
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A few optimizations

Commits
-------

ea633f5 [HttpKernel] Avoid updating the context if the request did not change
997d549 [HttpFoundation] Avoid a few unnecessary str_replace() calls
f5e7f24 [HttpFoundation] Optimize ServerBag::getHeaders()
merged branch Seldaek/methodmap (PR #7933)

This PR was merged into the master branch.

Discussion
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[DependencyInjection] Add a method map to avoid computing method names from service names

/cc @schmittjoh @stof

The diff is a bit messy because of indenting, but all this adds really is an `if(isset($this->methodMap[$id])) { $method = $this->methodMap[$id]; }` that bypasses the method_exists + strtr calls. It's not a huge improvements but saves some cycles on something that's typically called a few hundred times per request.

Commits
-------

f1c2ab7 [DependencyInjection] Add a method map to avoid computing method names from service names
[Crawler] Add proper validation of node argument of method add
merged branch entering/crawler-add-node-argument (PR #7924)

This PR was squashed before being merged into the master branch (closes #7924).

Discussion
----------

[Crawler] Add proper validation of node argument of method add

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

Crawler method add, fix PHPdoc and

Commits
-------

41805c0 [Crawler] Add proper validation of node argument of method add
fixed CS