You can clone with
HTTPS or Subversion.
1.4 branch is declared as Symfony 2.3 compatible, but the request param converter is already implementing 3.0's ParamConverterInterface (that's SensioFrameworkExtraBundle master branch).
You should branch these changes someway or remove the statement that 1.4 supports Symfony 2.4. composer.json states that 1.4 branch is Sf2.4 compatible too.
Perhaps you should add a note that on Sf2.4+ you should update the sensio/framework-extra-bundle dependency to 3.0.x@dev? Installs from symfony/framework-standard-edition base package are otherwise broken.