Merge branch 'core-updates'

doc: Add a "Boostrapping" section.

* doc/guix.texi (Package Modules): New node, with material formerly
  under "GNU Distribution".
  (Bootstrapping): New node.
* Makefile.am (EXTRA_DIST): Add doc/images/bootstrap-graph.dot and
  doc/images/bootstrap-graph.eps.
  (infoimagedir, dist_infoimage_DATA, DOT_OPTIONS): New variable.
  (.dot.png, .dot.eps, doc/guix.pdf, doc/guix.info, doc/guix.ps): New
  targets.
* doc/images/bootstrap-graph.dot: New file.