Merge branch 'ds/sparse-checkout-clean' into next

"git sparse-checkout" subcommand learned a new "clean" action to
prune otherwise unused working-tree files that are outside the
areas of interest.

* ds/sparse-checkout-clean:
  sparse-index: improve advice message instructions

Author: gitster

sparse-index.c

@@ -32,8 +32,9 @@ int give_advice_on_expansion = 1;
 	"Your working directory likely has contents that are outside of\n"     \
 	"your sparse-checkout patterns. Use 'git sparse-checkout list' to\n"   \
 	"see your sparse-checkout definition and compare it to your working\n" \
-	"directory contents. Running 'git sparse-checkout clean' may assist\n" \
-	"in this cleanup."
+	"directory contents. Cleaning up any merge conflicts or staged\n"      \
+	"changes before running 'git sparse-checkout clean' or 'git\n"         \
+	"sparse-checkout reapply' may assist in this cleanup."
 
 struct modify_index_context {
 	struct index_state *write;