fix "too much information" bug w/ "info vector" on PowerPC

[Paul Gilliam <pgilliam at us dot ibm dot com>]

Here is the problem:  When I do 'info vector', I get ALL the registers, not just the vector registers.
This happens because a test is made to see if a given register is in the vector group.   The test
compares the incoming register number against appropriate register numbers from tdep, ignoring
the fact that if, for example, there are no ev registers, the value of tdep->ppc_ev0_regnum will be
-1.  Same thing for tdep->ppc_vr0_regnum.

I was temped to commit this is obvious, but wanted the warm fuzzy of peer review.

-=# Paul #=-

2005-08-30  Paul Gilliam <pgilliam@us.ibm.com>

	* rs6000-tdep.c (rs6000_register_reggroup_p): don't assume that
        tdep->ppc_vr0_regnum or tdep->ppc_ev0_regnum are not -1


Index: rs6000-tdep.c
===================================================================
RCS file: /cvs/src/src/gdb/rs6000-tdep.c,v
retrieving revision 1.241
diff -3 -c -p -r1.241 rs6000-tdep.c
*** rs6000-tdep.c       25 May 2005 03:12:13 -0000      1.241
--- rs6000-tdep.c       30 Aug 2005 21:07:25 -0000
*************** rs6000_register_reggroup_p (struct gdbar
*** 1882,1890 ****
    if (group == float_reggroup)
      return float_p;

!   vector_p = ((regnum >= tdep->ppc_vr0_regnum
               && regnum < tdep->ppc_vr0_regnum + 32)
!             || (regnum >= tdep->ppc_ev0_regnum
                  && regnum < tdep->ppc_ev0_regnum + 32)
              || regnum == tdep->ppc_vrsave_regnum
              || regnum == tdep->ppc_acc_regnum
--- 1882,1892 ----
    if (group == float_reggroup)
      return float_p;

!   vector_p = ((tdep->ppc_vr0_regnum >= 0
!                && regnum >= tdep->ppc_vr0_regnum
               && regnum < tdep->ppc_vr0_regnum + 32)
!             || (tdep->ppc_ev0_regnum >= 0
!                   && regnum >= tdep->ppc_ev0_regnum
                  && regnum < tdep->ppc_ev0_regnum + 32)
              || regnum == tdep->ppc_vrsave_regnum
              || regnum == tdep->ppc_acc_regnum