Add github-domains config value for GitHub Enterprise setups, fixes #728

Signed-off-by: Gennady Feldman <gena01@gmail.com>
Updating ConfigCommand so that we can set github-domains from the command line.
First working version of GitHub Enterprise API.
Fixing broken unit test.
Validate the originUrl against the list of 'github-domains' from the config.
Refactoring my code to use a protected function to generate API Url.
Adding Config as parameter to the Driver::supports(), updating all drivers, user and tests.
Update 05-repositories.md

Typo, which is best addressed as a small rewrite.
Merge pull request #2376 from epeay/patch-1

Update 05-repositories.md
Per request from Jordi Boggiano (Seldaek) making Config 2nd parameter in supports()
added support for file:// url to repository

file:// is valid url even if it does not define a host.

allows to define a repo like this (local directory generated with
composer/satis):

```json
{
	"repositories": [ { "type": "composer", "url": "file:///home/cebe/dev/jescali/xeno-core/core/repo" } ],
	"require": {
        ...
	}
}
```
changes size of the line default value
Merge pull request #2387 from dyferencjal/inconsistent-io-interface

changes size of the line default value
Merge pull request #2386 from cebe/allow-file-url

added support for file:// url to repository
Remove dead code, fixes #2363
Merge pull request #2375 from gena01/github-ee

Fixing #728 Adding basic support for Github Enterprise
Fix target-dir update checks, fixes #2395
Retry on some 5xx errors

`composer install` gives me some intermittent 502 errors on github. Composer already does some retries. I think, on 502, 503 and 504, we should retry.
Merge pull request #2397 from smaftoul/patch-1

Retry on some 5xx errors
Fix authentication issue with subversion 1.8