MAINT: signal: Fix two build warnings in lfilter.c.src.
MAINT: signal: Fix two build warnings in lfilter.c.src.

* When building with Python 3, there was a pointer variable
  (char *s) that was not used.  The definition of the variable
  was moved into a block contained in the #else-#endif section
  of the #if-#else-#endif preprocesser statement.
* The second argument in a call to `PyArray_SetBase` had to be
  cast to `PyObject *`.

e-q/scipy,person142/scipy,jamestwebber/scipy,aarchiba/scipy,arokem/scipy,gertingold/scipy,andyfaff/scipy,matthew-brett/scipy,WarrenWeckesser/scipy,lhilt/scipy,scipy/scipy,Eric89GXL/scipy,mdhaber/scipy,jor-/scipy,tylerjereddy/scipy,ilayn/scipy,scipy/scipy,anntzer/scipy,lhilt/scipy,anntzer/scipy,andyfaff/scipy,Eric89GXL/scipy,rgommers/scipy,pizzathief/scipy,endolith/scipy,e-q/scipy,mdhaber/scipy,vigna/scipy,mdhaber/scipy,Stefan-Endres/scipy,perimosocordiae/scipy,grlee77/scipy,zerothi/scipy,matthew-brett/scipy,jor-/scipy,aeklant/scipy,aeklant/scipy,ilayn/scipy,Eric89GXL/scipy,andyfaff/scipy,mdhaber/scipy,andyfaff/scipy,tylerjereddy/scipy,endolith/scipy,nmayorov/scipy,aeklant/scipy,WarrenWeckesser/scipy,andyfaff/scipy,ilayn/scipy,vigna/scipy,tylerjereddy/scipy,vigna/scipy,grlee77/scipy,pizzathief/scipy,mdhaber/scipy,tylerjereddy/scipy,gertingold/scipy,zerothi/scipy,grlee77/scipy,perimosocordiae/scipy,e-q/scipy,rgommers/scipy,WarrenWeckesser/scipy,anntzer/scipy,aarchiba/scipy,pizzathief/scipy,zerothi/scipy,Stefan-Endres/scipy,Eric89GXL/scipy,WarrenWeckesser/scipy,rgommers/scipy,andyfaff/scipy,perimosocordiae/scipy,nmayorov/scipy,endolith/scipy,aarchiba/scipy,scipy/scipy,jor-/scipy,ilayn/scipy,person142/scipy,lhilt/scipy,zerothi/scipy,gertingold/scipy,pizzathief/scipy,aeklant/scipy,arokem/scipy,jor-/scipy,grlee77/scipy,endolith/scipy,grlee77/scipy,scipy/scipy,anntzer/scipy,WarrenWeckesser/scipy,e-q/scipy,Eric89GXL/scipy,tylerjereddy/scipy,jamestwebber/scipy,Stefan-Endres/scipy,pizzathief/scipy,aarchiba/scipy,ilayn/scipy,mdhaber/scipy,Stefan-Endres/scipy,Stefan-Endres/scipy,nmayorov/scipy,arokem/scipy,person142/scipy,arokem/scipy,ilayn/scipy,lhilt/scipy,aeklant/scipy,e-q/scipy,zerothi/scipy,jamestwebber/scipy,rgommers/scipy,vigna/scipy,anntzer/scipy,gertingold/scipy,person142/scipy,aarchiba/scipy,jamestwebber/scipy,Stefan-Endres/scipy,gertingold/scipy,jamestwebber/scipy,matthew-brett/scipy,perimosocordiae/scipy,vigna/scipy,scipy/scipy,perimosocordiae/scipy,scipy/scipy,Eric89GXL/scipy,person142/scipy,lhilt/scipy,nmayorov/scipy,anntzer/scipy,endolith/scipy,rgommers/scipy,jor-/scipy,WarrenWeckesser/scipy,endolith/scipy,arokem/scipy,matthew-brett/scipy,perimosocordiae/scipy,zerothi/scipy,matthew-brett/scipy,nmayorov/scipy