bpo-30532: Fix whitespace folding in certain cases

Leading whitespace was incorrectly dropped during folding of certain lines in the _header_value_parser's folding algorithm.  This makes the whitespace handling code consistent.
diff --git a/Misc/ACKS b/Misc/ACKS
index eaff172..89cd1fa 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -630,6 +630,7 @@
 Kelsey Hightower
 Jason Hildebrand
 Aaron Hill
+Joel Hillacre
 Richie Hindle
 Konrad Hinsen
 David Hobley
diff --git a/Misc/NEWS.d/next/Library/2017-06-26-11-01-59.bpo-30532.qTeL1o.rst b/Misc/NEWS.d/next/Library/2017-06-26-11-01-59.bpo-30532.qTeL1o.rst
new file mode 100644
index 0000000..adce85f
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2017-06-26-11-01-59.bpo-30532.qTeL1o.rst
@@ -0,0 +1 @@
+Fix email header value parser dropping folding white space in certain cases.