bug#19735: 25.0.50; regression: contrary to documentation etags does not work with compressed files any more; did work in emacs 24.4

[Gregor Zattler]

Dear emacs developers,

etags from emacs24 in debian jessie:
GNU Emacs 24.4.1 (i586-pc-linux-gnu, X toolkit, Xaw3d scroll
bars) of 2014-12-19 on brahms, modified by Debian

is able to work with e.g.
/usr/share/emacs/24.4/lisp/dired-aux.el.gz

while ~/src/emacs/lib-src/etags build from recent source is not:

$ ~/src/emacs/lib-src/etags /usr/share/emacs/24.4/lisp/dired-aux.el.gz
/usr/share/emacs/24.4/lisp/dired-aux.el.gz: Invalid argument

I did a git bisect on the emacs repository, this is the result:

first bad commit: [ba1ed52f0c2c7fd15fe1feadabfd0af88e19b4c3] Use binary-io 
module, O_BINARY, and „b“ flag.

There is already bug #2807: „etags can't access .el.gz files“
from 2009 which was confirmed and discussed but seemingly not
resolved in 2011.  bug #2807 describes that etags worked on the
compressed files but later it was not possible to use the TAGS
file.  The bug I file is about building the TAGS file.

Thanks for your attention, Gregor