source scl_source enable no longer works when using zsh

[TheFisherOne]

scl_source now uses == in if statements which is ok for bash but fails in zsh, this means that you can no longer use this in .zshrc

NOTE that a single = (which was all that was used in older versions of scl_source) works with bash and zsh

note that the documentation indicates that it is permissible to source scl_source in your .bashrc file. This used to also work in your .zshrc