Explain why @system-ca is seen in "show ssl ca-file".
Should fix issue #1979.
Can be backported till 2.6.
Display the list of CA files loaded into the process and their respective
certificate counts. The certificates are not used by any frontend or backend
until their status is "Used".
+ A "@system-ca" entry can appear in the list, it is loaded by the httpclient
+ by default. It contains the list of trusted CA of your system returned by
+ OpenSSL.
If a filename is prefixed by an asterisk, it is a transaction which
is not committed yet. If a <cafile> is specified without <index>, it will show
the status of the CA file ("Used"/"Unused") followed by details about all the