Patch context is applied as well

[SeverinLeonhardt]

Given file.txt:

a
b
c

And this patch (my.diff):

--- file.txt
+++ file.txt
@@ -1,3 +1,4 @@
 a
 b
+b1
 d

Which is applied using:

import patch
p = patch.fromfile("my.diff")
p.apply(".")

file.txt now looks like this:

a
b
b1
d

The patch only adds b1 but the following context was also put into the file. After applying the patch file.txt should not contain d but end with c.