Avoid potentially unportable parameter substitution in the test scripts.

tests/pio_write.run.in

 #!@SHELL@
 
-prefix=${0##*/}
+prefix=`echo "$0" | sed 's@.*/@@'`
 suffix=${suffix-grb}
 
 if ${mpi_task_num+:} false; then

tests/test_cksum_base.in

 # This file is meant to be included for the supported file formats.
 
-prefix=${0##*/}
+prefix=`echo "$0" | sed 's@.*/@@'`
 suffix=${suffix-grb}
 
 case ${suffix} in

tests/test_cksum_nc_chunk.run.in

 #!@SHELL@
 @ENABLE_NETCDF_FALSE@exit 77
 
-prefix=${0##*/}
+prefix='test_cksum_nc_chunk.run'
 format=nc
 @top_builddir@/libtool --mode=execute ${tool_wrap} ./cksum_write_chunk -b ${prefix} -m 17 || exit 1
 @top_builddir@/libtool --mode=execute ${tool_wrap} ./cksum_read ${prefix}.${format} ${prefix}.cksum || exit 1