Add a pep8 check to the makefile
Add a pep8 check to the makefile

Also reorganize the pyflakes check, since target dependencies do not
take the exit status of the shell command into account.

https://bugzilla.gnome.org/show_bug.cgi?id=672627

MathieuDuponchelle/pygobject,GNOME/pygobject,thiblahute/pygobject,jdahlin/pygobject,davibe/pygobject,GNOME/pygobject,GNOME/pygobject,davidmalcolm/pygobject,sfeltman/pygobject,davidmalcolm/pygobject,choeger/pygobject-cmake,pexip/pygobject,pexip/pygobject,MathieuDuponchelle/pygobject,choeger/pygobject-cmake,jdahlin/pygobject,davibe/pygobject,davidmalcolm/pygobject,davibe/pygobject,MathieuDuponchelle/pygobject,jdahlin/pygobject,sfeltman/pygobject,thiblahute/pygobject,choeger/pygobject-cmake,davibe/pygobject,pexip/pygobject,thiblahute/pygobject,sfeltman/pygobject