Fix indentation in c extension

Applied the GNU C coding convention to most files in the c extension.

The following settings were used with vim:

setlocal cindent
setlocal cinoptions=>4,n-2,{2,^-2,:2,=2,g0,h2,p5,t0,+2,(0,u0,w1,m1
setlocal sw=2
setlocal sts=2
setlocal tw=79
setlocal fo-=ro fo +=cql