prevent warnings when compiling with `gcc -Wextra`
prevent warnings when compiling with `gcc -Wextra`

The PyInt conversion functions generate two warnings when compiled under
`gcc -Wall -Wextra`:

1. comparison of unsigned expression < 0 is always false

2. signed and unsigned type in conditional expression

This patch fixes these problems by creating a new temporary variable
`is_unsigned`, which fixes problem 1, and by converting the ternary
return expression into a normal if/else branch, which fixes problem 2.

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