contrib/docker/centos6

revset: move order constants from revsetlang

Thanks to the recent refactor, the ordering rule is fully processed at
runtime.

FROM centos:centos6
RUN yum install -y gcc
RUN yum install -y python-devel python-docutils
RUN yum install -y make
RUN yum install -y rpm-build
RUN yum install -y gettext
RUN yum install -y tar
# For creating repo meta data
RUN yum install -y createrepo
# For python
RUN yum install -y readline-devel openssl-devel ncurses-devel zlib-devel bzip2-devel