Releases for X Autoload

Fix #2693315: "Call to undefined function apcu_fetch() in ApcuQueuedCachedClassLoader" if Self-updating APCu classmap is chosen but unavialable by dalin.

New cache type: Self-updating APCu classmap.

#2365781: Use of undefined constant DEBUG_BACKTRACE_IGNORE_ARGS
#2393205: Base table or view not found: 1146 Table 'system' doesn't exist when used in Profile

Stable release identical with 7.x-5.0-beta3.

* 1952498 Add DbCacheClassLoader.
* d2d842b Move test modules from VirtualFilesystem into real files in tests/fixtures/.modules.
* e5cfe91 Change libraries integration.
* b9a788f remove StaticCallLog stuff from where it doesn't belong.
* d3eb1cb Add a @see docblock.
* 7ee0916 Don't let ProxyClassFinder initialize twice.
* 6d96777 Document that AbstractCachedClassLoader::checkRequirements() returns true or false and does not throw an exception.
* 52f8f5b cleanup: linebreak at end of class.

New branch:

Bug fixes:
- #2195859: Installation error in PHP < 5.3.28 (?) (after I failed to include this fix in 7.x-4.3)
- #2228501: ProxyClassFinder not found Fatal Error (on Windows) by replacing all DIRECTORY_SEPARATOR with '/'.

Fix #2199913: Undefined Index: theme_engine

a6edb89 Fix hardcoded paths in DiscoveryTest::testWildcardFile
7fd74a7 The ServiceContainerInterface should have a __get() method.Finder().
0f70254 Add docblock and rename a parameter for Main::registerExtension() and Main::registerExtensionPsr4().

Absolute paths for Drupal modules, to fix #2162691: Unit tests: Relative paths given for autoload module's classes includes (Follow-up)

- Add xautoload_test_3 module in the web tests.
- Introduce CommonRegistrationInterface, so stuff like addPsr4() can be shared between class finder and adapter.

Fix web tests

New branch with PSR-4 support.

Fix #2078587: autoloading won't work during module install

Fix #1930084-2: Classes beginning with underscore

Re-added hook_xautoload().

New mechanic to resolve the situation where a registered directory does not exist.

xautoload loader should come after the core loaders, but before classloader.
Also, add an unregister() method to all loaders.
Only in unit tests need we prepend the class loader, to avoid hitting a malconfigured database with the core loader.

The 7.x-3.x branch brings some major architectural cleanup and rewrite.

Hotfix for a regression in 7.x-2.5 which made this module break if libraries is in 7.x-1.x branch.
See #1833382: Dependency on Libraries 2.x

Major new features:
- Introduction of hook_xautoload()
- Support for PSR-0 in sites/all/libraries with hook_libraries_info()
- Support discovery of test classes, including those in disabled modules.

Further changes:
- Added xautoload.api.php for documentation.
- Example module to demonstrate test loading
- Some trivial code changes and bug fixes

bug fixes.. see issue queue

Fixed the implementation of PSR-0, D8-style.
Added tests for PSR-0, D8-style.

Dev release for 7.x-2.x branch