Issue2495: tokenize.untokenize did not insert space between two consecutive string literals:
"" "" becomes """", which is invalid code.

Backport of r61979.
diff --git a/Lib/tokenize.py b/Lib/tokenize.py
index a9be4cf..0db3867 100644
--- a/Lib/tokenize.py
+++ b/Lib/tokenize.py
@@ -171,11 +171,12 @@
         t1 = [tok[:2] for tok in generate_tokens(f.readline)]
         newcode = untokenize(t1)
         readline = iter(newcode.splitlines(1)).next
-        t2 = [tok[:2] for tokin generate_tokens(readline)]
+        t2 = [tok[:2] for tok in generate_tokens(readline)]
         assert t1 == t2
     """
 
     startline = False
+    prevstring = False
     indents = []
     toks = []
     toks_append = toks.append
@@ -185,6 +186,14 @@
         if toknum in (NAME, NUMBER):
             tokval += ' '
 
+        # Insert a space between two consecutive strings
+        if toknum == STRING:
+            if prevstring:
+                tokval = ' ' + tokval
+            prevstring = True
+        else:
+            prevstring = False
+
         if toknum == INDENT:
             indents.append(tokval)
             continue