sslutil: try to find CA certficates in well-known locations Many Linux distros and other Nixen have CA certificates in well-defined locations. Rather than potentially fail to load any CA certificates at all (which will always result in a certificate verification failure), we scan for paths to known CA certificate files and load one if seen. Because a proper Mercurial install will have the path to the CA certificate file defined at install time, we print a warning that the install isn't proper and provide a URL with instructions to correct things. We only perform path-based fallback on Pythons that don't know how to call into OpenSSL to load the default verify locations. This is because we trust that Python/OpenSSL is properly configured and knows better than Mercurial. So this new code effectively only runs on Python <2.7.9 (technically Pythons without the modern ssl module).