Use filtered output in some dumping commands

There are several commands that may optionally send their output to a
file -- they take an optional filename argument and open a file.  This
patch changes these commands to use filtered output.  The rationale
here is that, when printing to gdb_stdout, filtering is appropriate --
it is, and should be, the default for all commands.  And, when writing
to a file, paging will not happen anyway (it only happens when the
stream==gdb_stdout), so using the _filtered form will not change
anything.