sslutil: guard against broken certifi installations (issue5406)...
sslutil: guard against broken certifi installations (issue5406)
Certifi is currently incompatible with py2exe; the Python code for certifi gets
included in library.zip, but not the cacert.pem file - and even if it were
included, SSLContext can't load a cacert.pem file from library.zip.
This currently makes it impossible to build a standalone Windows version of
Mercurial.
Guard against this, and possibly other situations where a module with the name
"certifi" exists, but is not usable.