improve detection of the extension suffix for cython_inline
improve detection of the extension suffix for cython_inline

reliance on imp.get_suffixes()[0] broke cython_inline on Debian systems
with support of multiarch where the first entry corresponded to the multiarch
suffix while distutil were using non-multiarch version while actually building
the extension

Reference: http://mail.python.org/pipermail//cython-devel/2012-July/002933.html

Now it would cache the suffix used by distutils and reuse it within the
session

andreasvc/cython,dahebolangkuan/cython,scoder/cython,ABcDexter/cython,hhsprings/cython,encukou/cython,fperez/cython,roxyboy/cython,mcanthony/cython,encukou/cython,fabianrost84/cython,dahebolangkuan/cython,hickford/cython,ChristopherHogan/cython,mrGeen/cython,roxyboy/cython,mrGeen/cython,JelleZijlstra/cython,c-blake/cython,cython/cython,larsmans/cython,mcanthony/cython,andreasvc/cython,larsmans/cython,larsmans/cython,roxyboy/cython,ABcDexter/cython,madjar/cython,cython/cython,mcanthony/cython,slonik-az/cython,marscher/cython,achernet/cython,achernet/cython,JelleZijlstra/cython,fabianrost84/cython,larsmans/cython,hhsprings/cython,andreasvc/cython,fabianrost84/cython,marscher/cython,da-woods/cython,ABcDexter/cython,slonik-az/cython,slonik-az/cython,c-blake/cython,achernet/cython,madjar/cython,andreasvc/cython,mrGeen/cython,slonik-az/cython,dahebolangkuan/cython,ABcDexter/cython,fperez/cython,acrispin/cython,ABcDexter/cython,achernet/cython,c-blake/cython,acrispin/cython,achernet/cython,hhsprings/cython,JelleZijlstra/cython,scoder/cython,JelleZijlstra/cython,mrGeen/cython,mrGeen/cython,larsmans/cython,encukou/cython,scoder/cython,JelleZijlstra/cython,c-blake/cython,slonik-az/cython,ChristopherHogan/cython,fperez/cython,andreasvc/cython,hickford/cython,fabianrost84/cython,madjar/cython,scoder/cython,acrispin/cython,dahebolangkuan/cython,madjar/cython,encukou/cython,madjar/cython,marscher/cython,marscher/cython,acrispin/cython,roxyboy/cython,hickford/cython,cython/cython,roxyboy/cython,mcanthony/cython,ChristopherHogan/cython,mcanthony/cython,encukou/cython,hhsprings/cython,c-blake/cython,fperez/cython,acrispin/cython,marscher/cython,dahebolangkuan/cython,hickford/cython,da-woods/cython,da-woods/cython,cython/cython,fabianrost84/cython,da-woods/cython,fperez/cython,hickford/cython,hhsprings/cython