Subdirectories without BUILD-INFO.txt cause Internal Server Errors

To add a bit of debugging info: if we look at http://snapshots.linaro.org/android/~linaro-android/origen-jb-gcc47-samsunglt-tracking-blob/44/MANIFEST and http://snapshots.linaro.org/android/~linaro-android/origen-jb-gcc47-samsunglt-stable-blob/98/MANIFEST, we can see the list of files being generated.

As such, it's possible that HOWTO support is actually to blame for this.

Copying the files locally in the same structure gives me this:

Traceback:
File "/usr/lib/python2.7/dist-packages/django/core/handlers/base.py" in get_response
  111. response = callback(request, *callback_args, **callback_kwargs)
File "/home/danilo/linaro/linaro-license-protection/both-eula-and-build-info/license_protected_downloads/views.py" in file_server
  404. {'dirlist': dir_list(url, path),
File "/home/danilo/linaro/linaro-license-protection/both-eula-and-build-info/license_protected_downloads/views.py" in dir_list
  109. license_digest_list = is_protected(pathname)
File "/home/danilo/linaro/linaro-license-protection/both-eula-and-build-info/license_protected_downloads/views.py" in is_protected
  224. build_info = BuildInfo(path)
File "/home/danilo/linaro/linaro-license-protection/both-eula-and-build-info/license_protected_downloads/buildinfo.py" in __init__
  23. self.readFile()
File "/home/danilo/linaro/linaro-license-protection/both-eula-and-build-info/license_protected_downloads/buildinfo.py" in readFile
  53. with open(self.build_info_file, "r") as infile:

Exception Type: IOError at /98/target/product/origen
Exception Value: [Errno 2] No such file or directory: u'/tmp/98/target/product/origen/howto/BUILD-INFO.txt'

Affects other builds also which are generating BUILD-INFO.txt :

http://snapshots.linaro.org/android/~linaro-android/panda-jb-gcc47-tilt-tracking-blob/107/target/product/pandaboard
http://snapshots.linaro.org/android/~linaro-android/snowball-jb-gcc47-igloo-stable-blob/118/target/product/snowball

Also observed on ARM Versatile Express A9 Jelly Bean build:

https://android-build.linaro.org/builds/~linaro-android/vexpress-jb-gcc47-armlt-tracking-open/#build=98

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