catch overflows in f.subs() where f is a libsingular polynomial
Merge branch 'develop' into trac_12718
fixed SIGSEGV when calling subs on 0
shut up Cython warnings about complicated declarations
Trac #12718: polynomial substitution overflow hell (libsingular bug?)

{{{
sage: R.<x,y> = QQ[]
sage: n=1000; f = x^n; f.subs(x = x^n)
x^1000000
sage: n=100000; f = x^n; f.subs(x = x^n)
x^1410065408*y^2
}}}

URL: http://trac.sagemath.org/12718
Reported by: was
Ticket author(s): Martin Albrecht
Reviewer(s): Volker Braun, William Stein