Merge r1872732, r1872777, r1874128, r1874190, r1874256, r1874542, r1874716, r1874720, r1874775, r1875465 from trunk:Non-x86 testing seems reasonably reliable; note some known failurescurrently.Add Travis job with --enable-mods-static=reallyall.Back off a little when svn export is timing out.Add Travis job which runs under UBSan ("Undefined Behaviour Sanitizer").mod_http2 disabled for now until https://github.com/icing/mod_h2/pull/194is merged.Add gcc 9 job, enable enhanced malloc debugging for pool-debug job.Add an i386 build using a multilib packages and "gcc -m32".(All other Travis builds are 64-bit arches currently)Switch to using httpd-tests git repo.Fix travis config validation warnings.Update docs. The expr_string.t failure has not been seen since the workaround was added AFAICT. The async filter bugis still breaking the tests regularly. [skip ci].Add simple test for apxs to catch regression in r1872042.