[Bug-readline] please rename xmalloc

[Tom Tromey]

Hi.

Right now, readline exports "xmalloc" and "xrealloc".  I think it would
be better if these were renamed to be in the readline namespace.

Currently gdb provides its own xmalloc in the main executable.  This
overrides the readline xmalloc.  However, while experimenting with
removing gdb's copy in favor of the libiberty xmalloc, I tripped across
the readline copy.  Having gdb use libiberty's fails because then gdb
tries to link against two libraries that each provide their own xmalloc.

I can send a readline patch if you think this is acceptable.
I'd suggest rl_malloc and rl_realloc as new names.

thanks,
Tom