Avoid rereading shared libraries that haven't changed.

	Avoid rereading shared libraries that haven't changed.

	* solib.c (free_so_symbols): New function, from ...
	(free_so): ... here.  Call it.
	(solib_read_symbols): Don't warn here if symbols have already been
	loaded.
	(solib_add): Warn here instead, if a pattern was specified.
	(reload_shared_libraries_1): New.
	(reload_shared_libraries): Rewrite to not fetch the library list.