Use filtered printing when reading symbols

Use filtered printing when reading symbols

While working on this series, I found some unfiltered prints that
didn't make sense -- many things, like complaints, are filtered, while
their context (in this case the "Reading symbols ..."  messages) may
not be.

This patch changes some spots in symbol reading to use filtered
prints.  I think this is preferable overall; in fact I'd go farther
and say that unfiltered printing should just be removed.

One of these spots was not strictly related (the change to
dump_psymtab), but I left it in partly because it makes psymtab.c
"unfiltered-clean", and partly because it is an example of filtered
and unfiltered printing being mixed in the same function.

gdb/ChangeLog
2018-10-04  Tom Tromey  <tom@tromey.com>

	* symfile.c (symbol_file_add_with_addrs, symbol_file_clear)
	(separate_debug_file_exists, find_separate_debug_file)
	(add_symbol_file_command, reread_symbols, allocate_symtab)
	(allocate_compunit_symtab): Use filtered printing, not
	unfiltered.
	* psymtab.c (require_partial_symbols, dump_psymtab)
	(allocate_psymtab): Use filtered printing, not unfiltered.