Fix archive script to set timestamps properly for .tar.gz

By default they are set to Jan 1 1970 which breaks homebrew.

Fixes #124.

tests/archive.py

 import os.path
 import sys
 import tarfile
+import time
 import zipfile
 import StringIO
 
@@ -29,6 +30,7 @@ def write_tar(target, arcprefix, sources, compression):
 			path = os.path.join(arcprefix, source)
 			info = tarfile.TarInfo(path)
 			info.size = len(data)
+			info.mtime = time.time()
 			archive.addfile(info, StringIO.StringIO(data))
 
 if len(sys.argv) < 4:
@@ -43,4 +45,4 @@ if target.endswith('.zip'):
 elif target.endswith('.tar.gz') or target.endswith('.tar.bz2'):
 	write_tar(target, arcprefix, sources, compression = os.path.splitext(target)[1][1:])
 else:
-	raise NotImplementedError('File type not supported: ' + target)
\ No newline at end of file
+	raise NotImplementedError('File type not supported: ' + target)