PR 7536 is about the fact that GDB lets the user set the input radix to
0 or 1, although claims it doesn't:

  (gdb) set input-radix 1
  Nonsense input radix ``decimal 1''; input radix unchanged.
  (gdb) show input-radix 
  Default input radix for entering numbers is 1.
  (gdb) set output-radix 1
  Invalid number "1".
  (gdb)

output-radix has similar problems.  This patch fixes both, and adds a
new test to radix.exp.

Checked in, after making sure there were no regressions
on x86_64-linux.

-- 
Pedro Alves