FIXME
  * doublecheck all deprecated vars - especially how they resolve!
  * Verify that all deprecations are fixable with only public variables.

Misc ideas...
  * Move sanity checks to testsanity target.
  * Use shell assignment operator != instead of = $(shell ...).
  * avoid confusing variables _cdbs_expand_$p_allflavors and
    _cdbs_expand_$p_defaultflavor.
  * Simplify build-dependencies separately from splitting systems from implementations.

  * strip tabs in middle of lines

  * && at start of line

  * avoid shell tests (use wildcard) in autotools-files.mk.in.

  * avoid copyright check on arch-only builds.
    Thanks to Matthias Klose (see bug#717827).

Ideas for 2nd epoch (i.e. /usr/share/cdbs/2/* files):

  * Support parallel build of self (i.e. avoid .NOTPARALLEL)
  * Consistent variable handling:
    + uppercase for overridable, lowercase for read-only
    + leading deb_ for package-specific, cdbs_ for global
    + allow early override (or register as special case)
    + always resolve *_ALL and *_$(pkg) for deb_* vars
  * Use only early resolved ifeq constructs when deliberate
  * enable regression tests by default
  * enable parallel build by default
  * Make auto-discovered docs easier overridable: Add collection to new
    variable DEB_INSTALL_DOCS (not DEB_INSTALL_DOCS_ALL).
    Closes: bug#207775.
  * Mention replacement variable in deprecation warnings.
