mk-ca-bundle.pl: switched to using hg.mozilla.org

... as mxr.mozilla.org is due to be retired.

The new host doesn't support If-Modified-Since nor ETags, meaning that
the script will now defer to download and do a post-transfer checksum
check to see if a new output is to be generated. The new output format
will hold the SHA1 checksum of the source file for that purpose.

We call this version 1.22

Reported-by: Ed Morley
Bug: http://curl.haxx.se/bug/view.cgi?id=1409