When running in an emacs shell buffer, if no packages are really going
to ask a question, the warning below should be printed only once, if
indeed at all.

Wouldn't it be better to print the below warning only upon something
intending to actually interact with the user?

Else if no questions are going to be asked by debconf, the warning is
irrelevant.

Setting up sqlite3 (3.8.7-1) ...
Setting up mailutils-common (1:2.99.98-2) ...
Setting up libmailutils4:i386 (1:2.99.98-2) ...
Setting up exim4-config (4.84-3) ...
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
Setting up netbase (5.3) ...
Installing new version of config file /etc/services ...
Setting up exim4-base (4.84-3) ...
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
Setting up exim4-daemon-light (4.84-3) ...
debconf: unable to initialize frontend: Dialog
debconf: (Dialog frontend will not work on a dumb terminal, an emacs shell buffer, or without a controlling terminal.)
debconf: falling back to frontend: Readline
Setting up mailutils (1:2.99.98-2) ...
Setting up bsdmainutils (9.0.6) ...
Setting up tzdata-java (2014h-2) ...
Setting up libapt-pkg4.12:i386 (1.0.9.3) ...