Update download page

 * Re-added link to Buildbot snapshot generator
 * Updated a few links
Update links to related projects
GitHub issues can also be used to report HCL updates
HCL: update CyberPower entries, including CP900AVR

Reported by Craig Duttweiler

Reference: http://news.gmane.org/find-root.php?message_id=%3c51295F86.4080601%40twistedsanity.net%3e
asciidoc: ignore all generated blazer*.html files
Replace 'connexion' with 'connection' in English contexts

Also reworded a few phrases surrounding the replacements.
HCL: Atlantis Land A03-P551(V1.2) supported by blazer_usb

Reported by Giovanni Panozzo.

Reference: http://news.gmane.org/find-root.php?message_id=%3c51B76B0C.1080109%40panozzo.it%3e

Note that blazer_usb will eventually be replaced by nutdrv_qx.
HCL: StarPower PCF-800VA

Reported by Don.

Reference: http://news.gmane.org/find-root.php?message_id=%3cCAPO%2bLDnApF3ALNfp%5fwaVpHqSuJ9sajKCKXPXLLsAWUWww7Of%3dw%40mail.gmail.com%3e
Update NEWS and UPGRADING for 2.7.1

Closes: networkupstools#37
Bump version to 2.7.1-pre2