Merge branch 'stable-2.6'

* stable-2.6:
  Add clarifications in the documentation of the `query` command
  Fix RebaseIfNecessary submit strategy
  Clarify setup of change cache in documentation

Conflicts:
	gerrit-server/src/main/java/com/google/gerrit/server/changedetail/RebaseChange.java

Change-Id: I24a16fdb6554b12a2da43b7874b36d77cc97e428
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>