Fix Python 2.6 error caused by Markdown updates

Markdown does not support Python 2.6 since version 2.5.0. Thus,
use Markdown<2.5.0 in Travis tests for Python 2.6.

.travis.yml

@@ -10,6 +10,8 @@ env:
     - DJANGO="Django>=1.6,<1.7" SOUTH="South>=0.8.4" SORLTHUMBNAIL="sorl-thumbnail>=11.12.1b"
     - DJANGO="https://www.djangoproject.com/download/1.7.b4/tarball/" SOUTH="" SORLTHUMBNAIL="sorl-thumbnail>=11.12.1b"
 install:
+  - if [[ $TRAVIS_PYTHON_VERSION == 2.6 ]]; then pip install "markdown>2.2.0,<2.5.0"; fi
+  - if [[ $TRAVIS_PYTHON_VERSION != 2.6 ]]; then pip install "markdown>2.2.0"; fi
   - pip install $DJANGO $SOUTH $SORLTHUMBNAIL -r .travis/requirements.txt
 matrix:
     exclude:

.travis/requirements.txt

@@ -2,8 +2,7 @@
 
 # sorl-thumbnail requirement is set in .travis.yml or requirements.txt
 
-# Wiki language processor
-Markdown>2.2.0
+# Markdown requirement is set in .travis.yml or requirements.txt
 
 # Package for flexible block handling
 django-sekizai>=0.7

requirements.txt

@@ -9,5 +9,10 @@ sorl-thumbnail>=11.12.1b
 # Migrations in Django
 South>=0.8.4
 
+# Wiki language processor
+# For Python 2.6, use Markdown<2.5.0, see
+# https://github.com/waylan/Python-Markdown/issues/349
+Markdown>2.2.0
+
 # Use requirements that are common with Travis tests
 -r .travis/requirements.txt