Daily builds not updating Pyrex generated C source

In r5731 changes were made to the signatures of some functions in diff-delta.c and the Pyrex code in _groupcompress_pyx.pyx that uses them. This seems to have broken the daily builds:

<https://code.launchpad.net/~bzr/+archive/daily/+buildjob/2420152>

building 'bzrlib._groupcompress_pyx' extension
gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -g -O2 -fPIC -I/usr/include/python2.6 -c bzrlib/_groupcompress_pyx.c -o build/temp.linux-i686-2.6/bzrlib/_groupcompress_pyx.o
bzrlib/_groupcompress_pyx.c: In function '__pyx_f_6bzrlib_18_groupcompress_pyx_10DeltaIndex_add_delta_source':
bzrlib/_groupcompress_pyx.c:602: error: too few arguments to function 'create_delta_index_from_delta'
bzrlib/_groupcompress_pyx.c: In function '__pyx_f_6bzrlib_18_groupcompress_pyx_10DeltaIndex_add_source':
bzrlib/_groupcompress_pyx.c:748: error: too few arguments to function 'create_delta_index'
bzrlib/_groupcompress_pyx.c: In function '__pyx_f_6bzrlib_18_groupcompress_pyx_10DeltaIndex__populate_first_index':
bzrlib/_groupcompress_pyx.c:818: error: too few arguments to function 'create_delta_index'
bzrlib/_groupcompress_pyx.c: In function '__pyx_f_6bzrlib_18_groupcompress_pyx_10DeltaIndex_make_delta':
bzrlib/_groupcompress_pyx.c:958: error: too few arguments to function 'create_delta'

  Cannot build extension "bzrlib._groupcompress_pyx".
  Use "build_ext --allow-python-fallback" to use slower python implementations instead.

error: command 'gcc' failed with exit status 1
dh_auto_build: python setup.py build returned exit code 1

What's confusing here is that python-pyrex is pulled in by apt, but apparently the C files are not being updated. There are messages output using `print` if there are import issues, are these perhaps being lost, unlike the `distutils.log` messages during the build?