httputil: set the headers before writing them

Change-Id: Ibb7db1ca06744b64ec29664059364fe7a1e8e837
Merge "httputil: set the headers before writing them"
search: IntConstraint
search: optimize ClaimList.Less sort. duh.
search: rename AttributeConstraint to PermanodeConstraint, add ModTime constraint
Merge branch 'master' of https://camlistore.googlesource.com/camlistore
pkg/index: use a map to populate the mutations

When indexing upon a blob reception, we first populate
all the mutations in a map instead of in a batch mutation.
Then we transfer all the mutations in a batch and commit
it immediately. This makes the window when the batch mutation
is open much shorter, and will ease future indexing because
it allows reading from the index while writing the mutations
to the map.

Change-Id: I276282388f59ca543835bfa5ec64986453b23fe1
Merge "pkg/index: use a map to populate the mutations"
search: change BlobMeta to have a CamliType, not a misleading MIMEType.

Change-Id: I1c6e111ef27aafd5a15f9b38746361093a78e9e6