ENH: special: make SpecialFunctionWarning always emitted by default

This should reduce confusion --- whether the warning is emitted or not
is already user-controlled by errprint(), and the default behavior of
Python warnings may be unexpected.

scipy/special/basic.py

@@ -13,6 +13,7 @@
 import types
 import specfun
 import orthogonal
+import warnings
 
 __all__ = ['agm', 'ai_zeros', 'assoc_laguerre', 'bei_zeros', 'beip_zeros',
            'ber_zeros', 'bernoulli', 'berp_zeros', 'bessel_diff_formula',
@@ -33,6 +34,7 @@
 
 class SpecialFunctionWarning(Warning):
     pass
+warnings.simplefilter("always", category=SpecialFunctionWarning)
 
 def errprint(inflag=None):
     _ufuncs_cxx._errprint(inflag)