Avoid "Package foo/* listed for update is not installed" error

Previously 'compose update foo/*' gave an error"Package foo/* listed for update is not installed. Ignoring" even if some foo/* packages were present; however the packages *would* then be updated as requested. 

This removes the false error iff foo/SOMEPACKAGE is required and would be updated.

Also refactors conversion of package name glob => regexp to one location in \Composer\Installer, and phpdoc's \Composer\Installer::$updateWhitelist

I have a vague idea there was an issue for this, but I can't find it :/