Modify error handeling for check_sequence to work with parallel computation

rpg/sequence.py

@@ -188,6 +188,6 @@ def check_sequence(seq):
     validate = seq.strip().upper()
     for i in validate:
         if i not in core.AMINOACIDS:
-            core.handle_errors("amino acid \"%s\" in %s not recognized." %
-                               (i, validate), 0, "Sequence ")
+            raise ValueError("amino acid \"%s\" in %s not "\
+                             "recognized." % (i, validate))
     return validate