patch: include newline at EOF in help text for interactive patch

The lack of a newline means that some "editors" that are useful in
tests, such as `echo "+new line" >> "$1"` don't work. It's obviously
easy to work around it, but newline at EOF seems like a good practice
anyway.

Differential Revision: https://phab.mercurial-scm.org/D6124

mercurial/patch.py

@@ -1117,7 +1117,8 b' the hunk is left unchanged.'
                     f = util.nativeeolwriter(os.fdopen(patchfd, r'wb'))
                     chunk.header.write(f)
                     chunk.write(f)
-                    f.write('\n'.join(['# ' + i for i in phelp.splitlines()]))
+                    f.write(''.join(['# ' + i + '\n'
+                                     for i in phelp.splitlines()]))
                     f.close()
                     # Start the editor and wait for it to complete
                     editor = ui.geteditor()