markdown: po4a tries to do some interpretation in code blocks

[Fat-Zer]

subj. At least it tries to interpret bullets.

---

How to reproduce:

foo.md:

```diff
-    .annotation system Ldalvik/annotation/Signature;
-    .end annotation
```

Run: po4a-updatepo -f text -o markdown -m foo.md -p foo.po

---

Actual result

foo.po:

...

#. type: Bullet: '-    '
#: foo.md:1
msgid ".annotation system Ldalvik/annotation/Signature;"
msgstr ""

#. type: Bullet: '-    '
#: foo.md:1
msgid ".end annotation"
msgstr ""

---

Expected result

...

#. type: Fenced code block
#: foo.md:2
#, no-wrap
msgid ""
"-    .annotation system Ldalvik/annotation/Signature;\n"
"-    .end annotation\n"
msgstr ""