sh -e behaviour was incorrect when && and || statements where used in
"if" clauses.
This is the patch submitted by MORI Kouji <mori@tri.asanuma.co.jp>.
It fixes the issue at hand, but sh fixes like this are super-hard to
verify that they don't break anything else. I ran some of my old test
cases and a few big GNU configure scripts that detected mistakes
before, with the previous sh, patched sh and bash. No differences in
behaviour found. MFC recommended after longer than usual time.