Bug#901808: debootstrap: --merged-usr is silently ignored on "blacklisted" suites like stretch
See the conversation around/following  for more context.
The TLDR is that the previous version of debootstrap allowed stretch to
be used with --merged-usr but the new implementation which turns on
merged-usr by default and blacklists anything stretch or older makes it
silently discard the explicit request from the user (without either an
error or warning that the flag is being ignored).
As noted by Ansgar in , debootstrap should instead default to
non-merged-usr for stretch and older, but it should be possible to
enable merged-usr via the command-line parameter (as debuerreotype now
always includes explicitly as of the 0.7 upload).
There is a pending merge request implementing this behavior at , and
I think the only points in question are whether defaulting the variable
to the empty string (and adjusting that empty default based on suite
later where we actually know it) is the desired approach and what to do
with EXTRACT_DEB_TAR_OPTIONS / adding "-k" (from bug 838388).
4096R / B42F 6819 007F 00F8 8E36 4FD4 036A 9C25 BF35 7DD4