- TDB::gc now only calls overwritePending when something changed.

- Removed TDB::gc calls from report.cpp.
- Made TDB::gc calls from task.cpp whenever necessary.
- Disabled TDB::gc calls when running a report for the sake of the shadow file.
- Shadow file overwrite now implemented using ostream, instead of cout.rdbuf trickery, for the well-being of cygwin.

src/TDB.cpp

@@ -486,8 +486,11 @@ int TDB::gc ()
     }
   }
 
-  // Dump all clean tasks into pending.
-  overwritePending (pending);
+  // Dump all clean tasks into pending.  But don't bother unless at least one
+  // task was transferred.
+  if (count)
+    overwritePending (pending);
+
   return count;
 }