Various fix and small improvements

[remicollet]

For discussion.

• Using exception seems a good idea.

At least it allow better test suite.
With this change, coverage is 100% for Dependency.php (~90% for Autoload.php)

• drop needed to ensure class if not already loaded in each autoloader (move it to main one)

[remicollet]

Fedora package (in rawhide) already have c781f66 and 9e2b39c

• composer and its dependencies use it
• PHPUnit use it
• php-fedora-autoloader now build correctly with PHPUnit
• php-symfony FTBFS is fixed

@siwinski have you time to review all this set of changes ? (perhaps time for a 0.2.0)

[siwinski]

@remi -- The biggest question I have regarding this is if we consider the following OK?:

try {
    \Fedora\Autoloader\Dependencies::required(array(
        '/a/required/dependency/that/does/not/exist/and/is/ignored.php',
    ));
} catch (Exception $e) {
}

[remicollet]

Indeed, using exception gives this feature (catching it)
I think this is OK, and a good improvement (best practices)