syntax-check: Add prohibit_space_in_label rule
syntax-check: Add prohibit_space_in_label rule

This guards against code such as

 cleanup :

which is happily accepted by the compiler but does not conform
to our style guidelines.

nertpinx/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,eskultety/libvirt,crobinso/libvirt,zippy2/libvirt,fabianfreyer/libvirt,zippy2/libvirt,taget/libvirt,libvirt/libvirt,nertpinx/libvirt,rlaager/libvirt,datto/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,rlaager/libvirt,libvirt/libvirt,olafhering/libvirt,crobinso/libvirt,datto/libvirt,crobinso/libvirt,eskultety/libvirt,rlaager/libvirt,jardasgit/libvirt,jfehlig/libvirt,taget/libvirt,nertpinx/libvirt,olafhering/libvirt,andreabolognani/libvirt,libvirt/libvirt,zippy2/libvirt,fabianfreyer/libvirt,crobinso/libvirt,eskultety/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,jfehlig/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,libvirt/libvirt,olafhering/libvirt,eskultety/libvirt,VenkatDatta/libvirt,datto/libvirt,andreabolognani/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,zippy2/libvirt,rlaager/libvirt,rlaager/libvirt,taget/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,taget/libvirt,andreabolognani/libvirt,eskultety/libvirt,nertpinx/libvirt,jardasgit/libvirt,taget/libvirt,datto/libvirt,datto/libvirt,nertpinx/libvirt,olafhering/libvirt