fabfile: update i18n helpers

Split the i18n helpers in two:
- one to update the source language (english) translation in
transifex
- one to get the update translations and compile them

This has been done so hopefully the translatable strings can
be updated more frequently and translators don't waste time
translating strings removed.

While at it add force options to tx pull as for some reason it
changed default behaviour to not override already available
translations which means to do nothing by default.

Author: xrmx

fabfile.py

@@ -6,12 +6,20 @@
 fabfile_dir = os.path.dirname(__file__)
 
 
-def i18n():
+def i18n_push_source():
+    """rebuild and push the source language to transifex"""
     with lcd('readthedocs'):
         local('rm -rf rtd_tests/tests/builds/')
-        local('tx pull')
-        local('django-admin makemessages --all')
+        local('django-admin makemessages -l en')
         local('tx push -s')
+
+
+def i18n_pull():
+    """pull the updated translation from transifex"""
+    with lcd('readthedocs'):
+        local('rm -rf rtd_tests/tests/builds/')
+        local('tx pull -f ')
+        local('django-admin makemessages --all')
         local('django-admin compilemessages')