Replace museum.php.net links with git.php.net

Hello,

since museum.php.net ist down ([Bug #68130](https://bugs.php.net/bug.php?id=68130) says it could take some weeks) I've replaced all links to it with links to source tarballs at git.php.net.
Unfortunately the file name can not received the download url, so I've added support for the `Content-Disposition` http header.

This PR should bring support for older PHP versions back to `php-build`
Yes. The methods aren't used anywhere else, so it shouldn't break anything.