Tell git to ignore python 2.6, which NaCl includes using DEPS on windows.

I considered removing the line to ignore python 2.4.  I left it in place in case anyone wants to check out an old version.

BUG=None
TEST=Run git gui on a chrome checkout under windows.  No longer see warnings about 7000+ untracked files.

Review URL: http://codereview.chromium.org/5519012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@68443 0039d316-1c4b-4281-b951-d872f2087c98

.gitignore

@@ -94,6 +94,7 @@ tags
 /third_party/ppapi
 /third_party/pthreads-win32
 /third_party/python_24
+/third_party/python_26
 /third_party/pywebsocket
 /third_party/safe_browsing/testing
 /third_party/skia