scons: Make scenario packer re-entrant and skip hidden files

This is the second attempt to fix Travis build failure

rsrc/SConscript

@@ -2,7 +2,7 @@
 from __future__ import print_function
 import os.path as path
 import subprocess, tarfile
-from os import walk as walk_dir, chdir
+from os import walk as walk_dir
 
 Import("env platform data_dir install_dir")
 
@@ -24,13 +24,12 @@ def pack_scenario(target, source, env):
 	for i in range(min(len(target), len(source))):
 		abspath = path.dirname(source[i].abspath)
 		with tarfile.open(target[i].abspath, 'w:gz') as tar:
-			for dir, subdirs, files in walk_dir('.'):
-				cur_dir = 'scenario' + dir[1:]
+			for dir, subdirs, files in walk_dir(abspath):
+				cur_dir = dir.replace(abspath, 'scenario')
 				for fname in files:
+					if fname.startswith('.'): continue
 					cur_file = path.join(cur_dir, fname)
-					chdir(abspath)
 					tar.add(path.join(dir, fname), arcname = cur_file)
-					chdir(prev_dir)
 
 env.Append(BUILDERS={"BuildScenario": Builder(action=pack_scenario, suffix=".boes", src_suffix="")})