make exif a submodule

Updates it to latest which includes a fix for a 100% hang on a jpg without any EXIF data:
https://www.dropbox.com/s/m5l185qxq9w5mzk/raspberry-pi-gpio-cheat-sheet.jpg

Signed-off-by: Alon Levy <alon@pobox.com>

mediagoblin/tools/exif.py

@@ -14,10 +14,11 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-try:
-    from EXIF import process_file, Ratio
-except ImportError:
-    from mediagoblin.tools.extlib.EXIF import process_file, Ratio
+import sys
+sys.path.append('extlib/exif')
+
+from EXIF import process_file
+from exifread.utils import Ratio
 
 from mediagoblin.processing import BadMediaFail
 from mediagoblin.tools.translate import pass_to_ugettext as _

mediagoblin/tools/extlib/EXIF.py

@@ -1 +0,0 @@
-../../../extlib/exif/EXIF.py