Fix #1050: Fix one known and some potential setting name conflicts.

Since sbt identifies settings and tasks by name, they must be
unique globally amonst all plugins in the world. This commit
renames some of the tasks and settings that would most likely
cause troubles while not being used much in builds.
Merge pull request #1053 from sjrd/prefix-setting-names

Fix #1050: Fix one known and some potential setting name conflicts.