core files in testsuite directory

[Michael Elizabeth Chastain]

drow> If the other tests _are_ supposed to generate core files (I don't
drow> know), then they should probably run in similar subdirectories.

Sounds good to me (but I admit I haven't looked at the code).

Also I regret that I approved gdb.c++/annota3.exp with the same
name as gdb.base/annota3.exp.  Dunno if we can move it now.
Certainly gdb.cp/annota3.exp has very little history to lose.

Michael C