Add overloads of read_until and async_read_until that take a string. Fix

bug in regex-based overload of async_read_until.


[SVN r34488]

libs/asio

@@ -1 +1 @@
-Subproject commit 5e2d09cdf29b17bdc2b00fa5540343f240d8efd8
+Subproject commit 72dfeb78e5f27ce7982675c67fe847a787b73f13