Building manuals in the source directory made sense when info manuals (and generated Texinfo sources used to build them, I think) were included in release tarballs (as still mentioned, inaccurately, in install.texi: "The distribution already includes the on-line formatted version of the manual, as Info files. You can regenerate those with @w{@code{make info}}, but it shouldn't be necessary."). Now "make dist" uses "git archive" and these files do not go in the tarballs. It would seem appropriate to build all formats of documentation (other than the special INSTALL and NOTES files) in the build directory only (removing manual/.gitignore).
This is fixed now in git with: commit e3945c47bdac1149a1fec5d46bd567a248cd17b9 Author: Andreas Jaeger <aj@suse.de> Date: Fri May 4 13:13:57 2012 +0200 Do not build manual in the source directory [BZ #13750] Build the manual in the build directory and not anymore in the source directory. I'll update install.texi now as well...
I had to remove the last patch and committed now an improved version: commit 6a4888ffd67163b589e602d62ca6330a608d8b89 Author: Andreas Jaeger <aj@suse.de> Date: Mon May 14 21:45:48 2012 +0200 Do not build manual in source dir [BZ #13750] Do not build manual anymore in the source dir. Also clean up the Makefile and remove rules that have been used previously when we had a stand-alone Makefile which was obsoleted recently.