[RFA, doc RFA] Avoid calling gdb_realpath if basenames are different

[Joel Brobecker]

> Ok to check in?
> 
> 2011-11-14  Doug Evans  <dje@google.com>
> 
>         * NEWS: Mention new parameter basenames-may-differ.
>         * dwarf2read.c (dw2_lookup_symtab): Avoid calling gdb_realpath if
>         ! basenames_may_differ.
>         * psymtab.c (lookup_partial_symtab): Ditto.
>         * symtab.c (lookup_symtab): Ditto.
>         (basenames_may_differ): New global.
>         (_initialize_symtab): New parameter basenames-may-differ.
>         * symtab.h (basenames_may_differ): Declare.

Looks good to me.

-- 
Joel