[1.0.X] Added some better error reporting and path handling when creating template paths.

We now raise UnicodeDecodeError for non-UTF-8 bytestrings (thanks to Daniel
Pope for diagnosing this was being swallowed by ValueError) and allow UTF-8
bytestrings as template directories. (The last bit is arguably a feature-add,
but we allow UTF-8 bytestrings everywhere else, so I'm counting it as a bugfix.)

Refs #8965.

Backport of r9161 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9162 bcc190cf-cafb-0310-a4f2-bffc1f526a37