Merge pull request #221 from s0undt3ch/develop

Make use of the new salt paths install options
[gentoo] started removing hard-coded keywording of salt dependencies + salt itself, as this all can be handled by Portage itself without having to keep track of dependencies in the bootstrap script once a new salt version is available.
[gentoo] don't install git explicitely, as this is already covered as dependency in the git-2.eclass which is inherited by the salt-9999.ebuild.
[gentoo] don't keyword the 9999 ebuild, this will be handled by Portage itself.
[gentoo] let 'emerge' unmask/keyword the required packages.
[gentoo] handle installing of the 9999/git salt ebuild.
[gentoo] include the package category when installing packages.
[gentoo] don't pollute the worldfile with non-explicitely requested packages.
[gentoo] make use of 'eix' where available.
[gentoo] bypass Portage's configuration file protection by adding the files to CONFIG_PROTECT_MASK to which 'emerge' might write to for installing possibly masked/keyworded packages/dependencies.
[gentoo] make sure existing content of CONFIG_PROTECT_MASK isn't overwritten.
[gentoo] CONFIG_PROTECT_MASK is space, not comma-delimited.
[gentoo] added comment wrt __gentoo_config_protection.
[gentoo] added support for systemd on Gentoo.
[gentoo] also apply the config protection bypass when installing the salt package itself, not only for its dependencies.
[gentoo] implemented suggested variant of detecting presence of 'eix'.
Merge pull request #228 from eliasp/gentoo-support

Improve Gentoo support
Update changes log and add Elias Probst(@eliasp) to authors.