[2nd try, RFC 0/2] Fix 'set remote XXX-limit -1' and 'set listisize'

[Yao Qi <yao at codesourcery dot com>]

Hi,
It was reported that my patch committed last month broke 'set remote
XXX-limit -1' by Khoo Yit Phang

  http://sourceware.org/ml/gdb-patches/2012-07/msg00702.html

and I proposed fix to this problem by adding a new type of 'var_type'
var_zuinteger_unlimited twice here,

  [RFC 0/3] New var_types var_zuinteger_unlimited
  http://sourceware.org/ml/gdb-patches/2012-08/msg00020.html

and

  [RFC 0/3] Get rid of var_integer in CLI
  http://sourceware.org/ml/gdb-patches/2012-08/msg00364.html

I feel that people are not convinced to add a new var_type
var_zuinteger_unlimited, so I decide to fix the problem in another way
(don't add new var_type).

Patch 1/2 adds the range check of command input, and patch 2/2 fixes
the inconsistency of the meaning of '0' and '-1' of 'listsize'.  I am
not sure it is a good idea to change the meaning of '0' and '-1' for
command 'set listsize' which has been used for many years, but it is
the best I can think of to fix the problem without adding new
var_type.  Comments are welcome.