Trac #15298: Two versions of QQ(sqrt{-1}) upon startup

We have two copies upon startup:
{{{
sage: import gc
sage: Ks=[K for K in gc.get_objects() if
....: isinstance(K,sage.rings.number_field.number_field.NumberField_quad
ratic)]
sage: [latex(k.0) for k in Ks]
[i, \sqrt{-1}]
}}}
I suspect they are coming from
`symbolic/pynac.pyx:2046 (in init_pynac_I)`
{{{
    K = QuadraticField(-1, 'I', embedding=CC.gen(), latex_name='i')
}}}
and from `rings/qqbar.py:7699 (in _init_qqbar)`
{{{
    QQbar_I_nf = QuadraticField(-1, 'I', embedding=CC.gen())
}}}
Should we perhaps both give them the same latex name so that these can
be the same field?

URL: https://trac.sagemath.org/15298
Reported by: nbruin
Ticket author(s): Frédéric Chapoton
Reviewer(s): Ralf Stephan

src/sage/rings/qqbar.py

@@ -2929,13 +2929,13 @@ def _latex_(self):
             sage: latex(AA(22/7))
             \frac{22}{7}
             sage: latex(QQbar(1/3 + 2/7*I))
-            \frac{2}{7} \sqrt{-1} + \frac{1}{3}
+            \frac{2}{7} i + \frac{1}{3}
             sage: latex(QQbar.zeta(4) + 5)
-            \sqrt{-1} + 5
+            i + 5
             sage: latex(QQbar.zeta(4))
-            \sqrt{-1}
+            i
             sage: latex(3*QQbar.zeta(4))
-            3 \sqrt{-1}
+            3 i
             sage: latex(QQbar.zeta(17))
             0.9324722294043558? + 0.3612416661871530? \sqrt{-1}
             sage: latex(AA(19).sqrt())
@@ -7576,7 +7576,7 @@ def _init_qqbar():
 
     AA_0 = AA.zero()
 
-    QQbar_I_nf = QuadraticField(-1, 'I', embedding=CC.gen())
+    QQbar_I_nf = QuadraticField(-1, 'I', embedding=CC.gen(), latex_name='i')
     QQbar_I_generator = AlgebraicGenerator(QQbar_I_nf, ANRoot(AAPoly.gen()**2 + 1, CIF(0, 1)))
     QQbar_I = AlgebraicNumber(ANExtensionElement(QQbar_I_generator, QQbar_I_nf.gen()))