Make writing to files work properly. (Fixes to BFD are also needed.)

Make writing to files work properly.  (Fixes to BFD are also needed.)

* core.c (core_open):  Open file ourselves, read or r/w, depending on
write_files.  Use bfd_fdopenr.
* gdbcore.h (write_files):  New variable.
* exec.c (write_files):  Define variable, add set&show for it.
(exec_file_command):  Use write_files to open for read or r/write.

Make shared library reading happen automatically.  These changes
are mostly from Peter Schauer <pes@regent.e-technik.tu-muenchen.de>.

* inferior.h (stop_soon_quietly):  Add to exported variables.
* infrun.c (child_create_inferior):  call solib hook, if defined.
(child_attach):  call solib hook, if defined.
* solib.c:  Include inferior.h.  Add from_tty to so_list as kludge.
(find_solib):  Use lookup_misc_func rather than hand-rolled.
(symbol_add_stub):  New stub for catch_errors.
(solib_add):  Avoid output if !from_tty.  Catch errors rather
than just calling symbol_file_add and bombing.
(solib_create_inferior_hook):  Interface with the target process
to let it read and alloc shared libs, then figure out what it did.

* core.c (validate_files):  Fix typo, soften warning.
(Fix from Hiroto Kagotani <kagotani@cs.titech.ac.jp>.)

* utils.c (fputs_demangled):  Avoid duplicate printing if
demangling is off.  (Fix from J.T. Conklin <jtc@cayenne.com>.)

* infrun.c (proceed):  Cast -1 to (CORE_ADDR) before comparing.
(Fix from pierre@la.tce.com (Pierre Willard).)

* main.c (catch_errors):  Change argument to a char * from an int,
since a char * can point to a struct full of glop, but an int
is not guaranteed to be able to hold a pointer.
* breakpoint.c (breakpoint_cond_eval, bpstat_stop_status,
breakpoint_re_set_one, breakpoint_re_set):  Adapt.
* core.c (core_open, solib_add_stub):  Adapt.
* remote-vx.c (symbol_stub, add_symbol_stub, callers):  Adapt.