Cody style: Fix spelling, e.g. "digest_tree" to "digestTree" and "inst" to "interest". Refs #2198.
code style: Renamed variable "co" to "data". Refs #2198.
code style: In ChronoSync2013, rename "usrseq_" to "sequenceNo_". Refs #2198.
Merge branch 'issue/2198-code-style-variables-spelling'. Refs #2198.
http://redmine.named-data.net/issues/2198