subtree: use "$*" instead of "$@" as appropriate

"$*" is for when you want to concatenate the args together,
whitespace-separated; and "$@" is for when you want them to be separate
strings.

There are several places in subtree that erroneously use $@ when
concatenating args together into an error message.

For instance, if the args are argv[1]="dead" and argv[2]="beef", then
the line

    die "You must provide exactly one revision.  Got: '$@'"

surely intends to call 'die' with the argument

    argv[1]="You must provide exactly one revision.  Got: 'dead beef'"

however, because the line used $@ instead of $*, it will actually call
'die' with the arguments

    argv[1]="You must provide exactly one revision.  Got: 'dead"
    argv[2]="beef'"

This isn't a big deal, because 'die' concatenates its arguments together
anyway (using "$*").  But that doesn't change the fact that it was a
mistake to use $@ instead of $*, even though in the end $@ still ended
up doing the right thing.

Signed-off-by: Luke Shumaker <lukeshu@datawire.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/subtree/git-subtree.sh

@@ -58,14 +58,14 @@ progress () {
 assert () {
 	if ! "$@"
 	then
-		die "assertion failed: " "$@"
+		die "assertion failed: $*"
 	fi
 }
 
 ensure_single_rev () {
 	if test $# -ne 1
 	then
-		die "You must provide exactly one revision.  Got: '$@'"
+		die "You must provide exactly one revision.  Got: '$*'"
 	fi
 }
 
@@ -690,7 +690,7 @@ cmd_add () {
 
 		cmd_add_repository "$@"
 	else
-		say >&2 "error: parameters were '$@'"
+		say >&2 "error: parameters were '$*'"
 		die "Provide either a commit or a repository and commit."
 	fi
 }