Doctest: Fix collect_common_factors() to accept any expression

[rwst]

Visible already in sage-7.1v, difficult to get a good minimal test case.

sage: (1/24*((sqrt(3)*2^(2/3)*gamma(1/3) + I*2^(2/3)*gamma(1/3))/pi + 4*2^(2/3)*gamma(1/3)/(pi*(sqrt(3) + I)))/x^(1/3)).collect_common_factors()
1/24*2^(2/3)*(sqrt(3) + 4/(sqrt(3) + I) + I)*gamma(1/3)/(pi*x^(1/3))
sage: (1/24*((I*2^(2/3)*gamma(1/3))/pi + 4*2^(2/3)*gamma(1/3)/(pi*(sqrt(3) + I)))/x^(1/3)).collect_common_factors()
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-6-c25fe41fc3c2> in <module>()
----> 1 _.collect_common_factors()

/home/ralf/sage-7.1v/src/sage/symbolic/expression.pyx in sage.symbolic.expression.Expression.collect_common_factors (/home/ralf/sage-7.1v/src/build/cythonized/sage/symbolic/expression.cpp:37782)()
   6649         sig_on()
   6650         try:
-> 6651             x = g_collect_common_factors(self._gobj)
   6652         finally:
   6653             sig_off()

ValueError: divide: arguments must be polynomials over the rationals

Depends on #23325

Component: symbolics

Author: Ralf Stephan

Branch/Commit: u/rws/doctest__fix_collect_common_factors___to_accept_any_expression @ 1597fed

Issue created by migration from https://trac.sagemath.org/ticket/21009

[rwst]

Description changed:

--- 
+++ 
@@ -16,6 +16,6 @@
    6652         finally:
    6653             sig_off()
 
-ValueError: gcd: arguments must be polynomials over the rationals
+ValueError: divide: arguments must be polynomials over the rationals
 ```
-It is not difficult to fix the symbolic gcd to accept any expression. The method is already implemented in Pynac's giac interface.
+

[rwst]

comment:2

We now get with Sage-8.0

sage: (1/24*((I*2^(2/3)*gamma(1/3))/pi + 4*2^(2/3)*gamma(1/3)/(pi*(sqrt(3) + I))
....: )/x^(1/3)).collect_common_factors()
....: 
1/24*2^(2/3)*(4/(sqrt(3) + I) + I)*gamma(1/3)/(pi*x^(1/3))

[rwst]

comment:3

Actually the fix was unintentional and is in Pynac-0.7.10. This will add doctests.

[rwst]

Dependencies: #23225