diff: '\ No newline at end of file' is also not part of the header

Diff containing '\ No newline at end of file' were colorized incorrectly.

mercurial/patch.py

@@ -1639,7 +1639,7 b' def difflabel(func, *args, **kw):'
                 if line.startswith('@'):
                     head = False
             else:
-                if line and not line[0] in ' +-@':
+                if line and not line[0] in ' +-@\\':
                     head = True
             stripline = line
             if not head and line and line[0] in '+-':