check system pari/gp for qfisom bug #2140

see
http://pari.math.u-bordeaux.fr/cgi-bin/bugreport.cgi?bug=2140

Author: dimpase

build/pkgs/pari/spkg-configure.m4

@@ -88,6 +88,17 @@ SAGE_SPKG_CONFIGURE([pari], [
            AC_MSG_NOTICE([Otherwise Sage will build its own pari/GP.])
            sage_spkg_install_pari=yes
         fi
+        AC_MSG_CHECKING([whether qfisom bug of pari 2.11.2 is fixed])
+        bug_check=`echo "qfisom([[16,6;6,10]],[[4,3;3,10]])" | $GP -qf 2>> config.log`
+        expected="0"
+        if test x"$bug_check" = x"$expected"; then
+           AC_MSG_RESULT([yes])
+        else
+           AC_MSG_RESULT([no; cannot use system pari/GP with known bug])
+           AC_MSG_NOTICE([Upgrade your system package and reconfigure.])
+           AC_MSG_NOTICE([Otherwise Sage will build its own pari/GP.])
+           sage_spkg_install_pari=yes
+        fi
     fi dnl end GP test
 
       if test x$sage_spkg_install_pari = xno; then dnl main PARI test