autoconfigure future warning

[mochrul]

While I tried to compile the zorp, I found this warning:

tests/unit/Makefile.am:11: warning: source file 'helpers/zproxy.cc' is in a subdirectory,
tests/unit/Makefile.am:11: but option 'subdir-objects' is disabled
automake: warning: possible forward-incompatibility.
automake: At least a source file is in a subdirectory, but the 'subdir-objects'
automake: automake option hasn't been enabled.  For now, the corresponding output
automake: object file(s) will be placed in the top-level directory.  However,
automake: this behaviour will change in future Automake versions: they will
automake: unconditionally cause object files to be placed in the same subdirectory
automake: of the corresponding sources.
automake: You are advised to start using 'subdir-objects' option throughout your
automake: project, to avoid future incompatibilities.

Automake is from debian unstable (Unpacking automake (1:1.15-4))