-pkg/server/share.go handles share(d) blobs.
-pkg/blobserver/gethandler no longer deals with share blobs
and has been rewritten like the other handlers (no more auth
in there).
-client and signhandler changed accordingly.
-serverconfig: auth moved up in makeCamliHandler
-share parameter added to the user level and low level config.
-share URL is now http(s)://host[:port]/[prefix/]share/sha1-xxxx.
Addresses http://camlistore.org/issue/107
Change-Id: I0a2c07ac1a1e435b141702e0ff06dc8182721d65
Brad Fitzpatrick