Hello,

a forwarded bug http://bugs.debian.org/646413

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The system installed certificates directory is not complete, so that
one may need to have additional certificates in one's own directory
and use the --ca-directory (either as a command-line option or via
the .wgetrc file). But if such an option is used, the system installed
certificates are no longer used, as documented in the wget man page,
meaning that wget will start to fail on various sites. For instance:

xvii:~> wget --ca-directory=$HOME/wd/config/cacert https://twitter.com/
--2011-10-24 02:29:31--  https://twitter.com/
Resolving twitter.com (twitter.com)... 199.59.148.10, 199.59.149.198, 199.59.149.230
Connecting to twitter.com (twitter.com)|199.59.148.10|:443... connected.
ERROR: The certificate of `twitter.com' is not trusted.
ERROR: The certificate of `twitter.com' hasn't got a known issuer.
zsh: exit 5     wget --ca-directory=$HOME/wd/config/cacert https://twitter.com/

xvii:~> wget https://twitter.com/
--2011-10-24 02:34:20--  https://twitter.com/
Resolving twitter.com (twitter.com)... 199.59.148.10, 199.59.149.198, 199.59.149.230
Connecting to twitter.com (twitter.com)|199.59.148.10|:443... connected.
HTTP request sent, awaiting response... 200 OK
[...]

There should be a way to fallback to the system installed certificates
directory. For instance, --ca-directory could contain a list of
directories (like $PATH-like environment variables), and if the
path ends with a ":", the default directories are appended.
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