lockfile: show absolute filename in unable_to_lock_message
lockfile: show absolute filename in unable_to_lock_message

When calling a git command from a subdirectory and a file locking fails,
the user will get a path relative to the root of the worktree, which is
invalid from the place where the command is ran. Make it easy for the
user to know which file it is.

Signed-off-by: Matthieu Moy <d4d2cc2a6ec7b2aa587d4887cc5ed200f9b685a1@imag.fr>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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