core-tutorial: adjust to recent reality.
core-tutorial: adjust to recent reality.

We still talked about HEAD symlinks but these days we use
symrefs by default.

Also 'failed/prevented' message is now gone from the merge
output.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git