serverconfig: conditionally install expvar handler.

Add local copy of the standard library's expvar handler.

Change-Id: Ida41553345d7d29665f33268356bf16a80386e38
Merge "serverconfig: conditionally install expvar handler."
Add generation support for diskpacked.

Maybe we should refactor the common code to pkg/blobserver/generation ?

Change-Id: Ib04125805d5a1960bd29a474d3fc7ca985708d8d
Merge branch 'master' of https://camlistore.googlesource.com/camlistore
Merge branch 'dp-generation'