logd: use coalesce instead of merge (cleanup)

- switch to coalesce instead of merge in naming of functions
  and variables. Confusing since we also to merge-sorts and
  other activities in the logger.
- define maxPrune rather than using a number in the code path.

Bug: 24511000
3 files changed
tree: c66a6426786b75c5a96b49f05a7de4c4bb2fc45b
  1. liblog/
  2. logcat/
  3. logd/
  4. logwrapper/