for #788; make the ndarr2str() function as fast as possible in 2.x
for #788; make the ndarr2str() function as fast as possible in 2.x

git-svn-id: 6d9763a5a770351123389058c013888add577529@16500 fe389314-cf27-0410-b35b-8c050e845b92

spacetelescope/stsci.tools