Version sharing (#465) + optional inclusion of subprojects in the roadmap view (...

Version sharing (#465) + optional inclusion of subprojects in the roadmap view (#2666).

Each version of a project can be shared with:
* subprojects
* projects in the project hierarchy: ancestors + descendants (needs versions management permission on the root project)
* projects in the project tree: root project + all its descendants (same as above)
* all projects (can be set by admin users only)

Notes:
* when sharing a version of a private project with others projects, its name will be visible within the other projects
* a project with versions used by non descendant projects can not be archived

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3123 e93f8b46-1217-0410-a6f0-8f06a7374b81