Remove useless uses of cat, and replace with filename arguments

Replace uses of cat that do nothing but writing the contents of
a single file to another command via pipe.

[jc: Original patch from Josh was somewhat buggy and rewrote
"cat $file | wc -l" to "wc -l $file", but this one should be Ok.]

Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-commit.sh

@@ -593,7 +593,7 @@ then
 		tree=$(GIT_INDEX_FILE="$TMP_INDEX" git write-tree) &&
 		rm -f "$TMP_INDEX"
 	fi &&
-	commit=$(cat "$GIT_DIR"/COMMIT_MSG | git commit-tree $tree $PARENTS) &&
+	commit=$(git commit-tree $tree $PARENTS <"$GIT_DIR/COMMIT_MSG") &&
 	rlogm=$(sed -e 1q "$GIT_DIR"/COMMIT_MSG) &&
 	git update-ref -m "$GIT_REFLOG_ACTION: $rlogm" HEAD $commit "$current" &&
 	rm -f -- "$GIT_DIR/MERGE_HEAD" "$GIT_DIR/MERGE_MSG" &&

git-filter-branch.sh

@@ -171,7 +171,7 @@ case "$filter_subdir" in
 	git rev-list --reverse --topo-order --default HEAD \
 		--parents --full-history "$@" -- "$filter_subdir"
 esac > ../revs
-commits=$(cat ../revs | wc -l | tr -d " ")
+commits=$(wc -l <../revs | tr -d " ")
 
 test $commits -eq 0 && die "Found nothing to rewrite"
 
@@ -241,7 +241,7 @@ case "$target_head" in
 	;;
 *)
 	git update-ref refs/heads/"$dstbranch" $target_head
-	if [ $(cat ../map/$src_head | wc -l) -gt 1 ]; then
+	if [ $(wc -l <../map/$src_head) -gt 1 ]; then
 		echo "WARNING: Your commit filter caused the head commit to expand to several rewritten commits. Only the first such commit was recorded as the current $dstbranch head but you will need to resolve the situation now (probably by manually merging the other commits). These are all the commits:" >&2
 		sed 's/^/	/' ../map/$src_head >&2
 		ret=1

git-ls-remote.sh

@@ -82,7 +82,7 @@ rsync://* )
 	(cd $tmpdir && find refs -type f) |
 	while read path
 	do
-		cat "$tmpdir/$path" | tr -d '\012'
+		tr -d '\012' <"$tmpdir/$path"
 		echo "	$path"
 	done &&
 	rm -fr $tmpdir

git-quiltimport.sh

@@ -70,10 +70,11 @@ tmp_info="$tmp_dir/info"
 commit=$(git rev-parse HEAD)
 
 mkdir $tmp_dir || exit 2
-for patch_name in $(cat "$QUILT_PATCHES/series" | grep -v '^#'); do
+for patch_name in $(grep -v '^#' < "$QUILT_PATCHES/series" ); do
 	echo $patch_name
-	(cat $QUILT_PATCHES/$patch_name | git mailinfo "$tmp_msg" "$tmp_patch" > "$tmp_info") || exit 3
-	test -s .dotest/patch || {
+	git mailinfo "$tmp_msg" "$tmp_patch" \
+		<"$QUILT_PATCHES/$patch_name" >"$tmp_info" || exit 3
+	test -s "$tmp_patch" || {
 		echo "Patch is empty.  Was it split wrong?"
 		exit 1
 	}