aclocal.m4 is autogenerated, so running aclocal would remove the
m4_include of acinclude.m4.
The exceptions are at the top of the source tree and in nsock/src, where
an acinclude.m4 lives; aclocal notices it there and automatically adds
an inclusion to the end of aclocal.m4, so no inclusion is needed in
configure.ac.
If you have trouble updating after this revision you need to follow
these instructions. You have probably just seen an error like this:
svn: URL 'svn://svn.insecure.org/nping' of existing directory 'nping'
does not match expected URL 'svn://svn.insecure.org/nmap/nping'
This is caused by the replacement of SVN externals.
Here's what you need to do. First, save any local changes you might have
in the nping, nsock, nbase, ncat, and zenmap directories. (For example
by running "cd nping; svn diff > ../nping.diff".) If you don't have any
local changes you can skip this step.
Then run these commands:
rm -rf nping/ nsock/ nbase/ ncat/ zenmap/
svn update
svn cleanup
If all else fails, you can just delete your whole working directory and
check out anew:
svn co --username guest --password "" svn://svn.insecure.org/nmap
There may be further discussion in the mailing list thread at
http://seclists.org/nmap-dev/2011/q4/303.
