merge-recursive: convert malloc / strcpy to strbuf

This would be a fairly routine use of xstrfmt, except that
we need to remember the length of the result to pass to
cache_name_pos. So just use a strbuf, which makes this
simple.

As a bonus, this gets rid of confusing references to
"pathlen+1". The "1" is for the trailing slash we added, but
that is automatically accounted for in the strbuf's len
parameter.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

merge-recursive.c

@@ -630,25 +630,24 @@ static char *unique_path(struct merge_options *o, const char *path, const char *
 
 static int dir_in_way(const char *path, int check_working_copy)
 {
-	int pos, pathlen = strlen(path);
-	char *dirpath = xmalloc(pathlen + 2);
+	int pos;
+	struct strbuf dirpath = STRBUF_INIT;
 	struct stat st;
 
-	strcpy(dirpath, path);
-	dirpath[pathlen] = '/';
-	dirpath[pathlen+1] = '\0';
+	strbuf_addstr(&dirpath, path);
+	strbuf_addch(&dirpath, '/');
 
-	pos = cache_name_pos(dirpath, pathlen+1);
+	pos = cache_name_pos(dirpath.buf, dirpath.len);
 
 	if (pos < 0)
 		pos = -1 - pos;
 	if (pos < active_nr &&
-	    !strncmp(dirpath, active_cache[pos]->name, pathlen+1)) {
-		free(dirpath);
+	    !strncmp(dirpath.buf, active_cache[pos]->name, dirpath.len)) {
+		strbuf_release(&dirpath);
 		return 1;
 	}
 
-	free(dirpath);
+	strbuf_release(&dirpath);
 	return check_working_copy && !lstat(path, &st) && S_ISDIR(st.st_mode);
 }