[REGRESSION] bzr 1.17 does not use _knit_load_data compiled extension

[Alexander Belchenko]

Hi,

While building my own custom installer for bzr.exe 1.17 I found that _knit_load_data_pyx C-extension
actually is not imported at all in bzrlib. Instead there is still attempts to import old name
"_knit_load_data_c" extension.

_knit_load_data_c was renamed to _knit_load_data_pyx by Vincent in bzr.dev revno 4472 but Vincent
did not update all imports. At least not in 1.17.

I don't know is it critical for performance (I suppose -- yes), but it does not sound right for me
anyway.