New option "set print symbol-loading".

	* NEWS: Mention it.
	* solib.c (solib_read_symbols): Only print symbol loading messages
	if requested.
	(solib_add): If symbol loading is in "brief" mode, notify user
	symbols are being loaded.
	(reload_shared_libraries_1): Ditto.
	* symfile.c (print_symbol_loading_off): New static global.
	(print_symbol_loading_brief): New static global.
	(print_symbol_loading_full): New static global.
	(print_symbol_loading_enums): New static global.
	(print_symbol_loading): New static global.
	(print_symbol_loading_p): New function.
	(symbol_file_add_with_addrs): Only print symbol loading messages
	if requested.
	(_initialize_symfile): Register "print symbol-loading" set/show
	command.
	* symfile.h (print_symbol_loading_p): Declare.

	doc/
	* gdb.texinfo (Symbols): Document set/show print symbol-loading.

	testsuite/
	* gdb.base/print-symbol-loading-lib.c: New file.
	* gdb.base/print-symbol-loading-main.c: New file.
	* gdb.base/print-symbol-loading.exp: New file.