libglusterfs: Return 'ERANGE' for ASCII string to number system

Using 'EOVERFLOW' should be limited to data structure
alignments not Number systems.

Change-Id: I7d337d414e998c0a729c95661df239e36c753a38
BUG: 1017746
Signed-off-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-on: http://review.gluster.org/6101
Reviewed-by: Kaushal M <kaushal@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>