Added error handling and error messages around missing perforce driver, invalid username/password
incorporated change to Perforce: Capture output, stopping errors showing up if p4 is not available
Merge pull request #2472 from vuhl/master

Added some error handling and error messages for common errors using Perforce driver
Check exclude from downloaded composer.json
Merge pull request #2482 from oziks/fix-composer-archive-property

Check exclude from downloaded composer.json
Check exception code only if class ZipArchive exists

If is for example exception throwed when downloading tar archive on system without installed zip extension, PHP hangs on fatal error " Class 'ZipArchive' not found".
Merge pull request #2483 from JakubOnderka/patch-2

Check exception code only if class ZipArchive exists
Detect ~> misuse and suggest fix, fixes #2476
Skip aliases packages when looking for plugins.
Merge pull request #2508 from simensen/plugin-manager-skips-alias-packages

Skip aliases packages when looking for plugins.
Make PluginManager::loadRepository public
Merge pull request #2510 from simensen/plugin-load-repository-made-public

Make PluginManager::loadRepository public