Allow If-None-Match header for storage requests

http://tools.ietf.org/html/draft-dejong-remotestorage-01 adds support
for conditional requests using the If-None-Match header. This change
fixes remotestorage.js 0.8 not working with restore due to using that
header by default.
Merge pull request #10 from skddc/master

Allow If-None-Match header for storage requests