build/remove protoc-c: not used and not useful
messagbus: unfinished, so build only with --enable-dev
build/header install: extract userpci, hostmot part of a86745d

a86745d is a bit much in one go, so do this piecemeal
m4/ac_pkg_cython.m4: remove misleading warning

we're just _testing_, not requiring cython, so there's no point in being
militant about it
configure/cython: mention if cython wasnt found - not a fatal config error

cython is only needed if any files *.pyx,*.pxd are modified or added.

since few people are likely to do this, there's no point in requiring
this package upfront.
hal/cython: add pre-cythonified .c files

this makes it unnecessary to install cython when not working on the
bindings.

Cython version was: 0.19.1+git34-gac3e3a2-1~bpo70+1 ,
installed with 'sudo apt-get -t wheezy-backports install cython'