SVN doesn't like requesting logs for non-existent revisions

If revisions 1-130 exist, it errors at "svn log -r 1:250", so we can't
reliably give a last number. Easiest solution is to just forego per-batch
processing, and fetch all the unseen entries in one go.

attract_server/subversion.py

@@ -12,7 +12,6 @@ from . import attrs_extra
 
 task_logged = blinker.NamedSignal('task_logged')
 task_marker_re = re.compile(r'\[(?P<task_id>T\d+)\]')
-FETCH_AND_OBSERVE_CHUNK_SIZE = 10
 
 
 def obtain(server_location):
@@ -33,8 +32,7 @@ class CommitLogObserver(object):
         self._log.debug('%s: fetch_and_observe()', self)
 
         svn_log = self.svn_client.log_default(
-            revision_from=self.last_seen_revision + 1,
-            revision_to=self.last_seen_revision + FETCH_AND_OBSERVE_CHUNK_SIZE)
+            revision_from=self.last_seen_revision + 1)
 
         for log_entry in svn_log:
             self._log.debug('- %r', log_entry)