While there, improve the params help text.

In the human monitor, it declares a single optional argument to be
parsed according to the QemuOptsList given by its name.

In QMP, it declares an optional argument for each member of the
QemuOptsList.

Restriction: only lists with empty desc are supported for now.  Good
enough for the job at hand.  We'll lift the restriction when we need
that.

Next commit wants to use it.

We sometimes permit omitting the first option name, for example
-device foo is short for -device driver=foo.  The name to use
("driver" in the example) is passed as argument to qemu_opts_parse().
For each QemuOptsList, we use at most one such name.

Move the name into QemuOptsList, and pass whether to permit the
abbreviation.  This ensures continued consistency, and simplifies the
commit after next in this series.

The functions are somewhat restricted.  Good enough for the job at
hand.  We'll extend them when we need more.

Conversion to QObject is still missing.

This reverts commit 3ced9f7a.

The next commit will convert all of qdev_device_add() to QError, and
it'll be clearer with this partial conversion reverted.

Treat multiple successive slashes as a one slash.  Ignore trailing
slashes.  This is how POSIX pathnames work.

Also put error definitions in alphabetical order

While fully converted handlers are not supposed to print anything when
running in a QMP monitor, they are free to print in a human monitor.
For instance, device_add (not yet converted) prints help, and will
continue to do so after conversion.

Moreover, utility functions converted to QError should remain usable
from unconverted handlers.

Two problems:

* handler_audit() complains when a converted handler prints.  Limit
  that to QMP monitors.

* With QMP, handlers need to pass the error object by way of
  monitor_set_error().  However, we do that both for QMP and for the
  human monitor.  The human monitor prints the error object after the
  handler returns.  If the handler prints anything else, that output
  "overtakes" the error message.

  Limit use of monitor_set_error() to QMP monitors.  Update
  handler_audit() accordingly.

Users can't set them, so qdev_device_help() shouldn't list them.  Fix
that.  Also make qdev_prop_parse() hide them instead of printing a
meaningless "has no parser" error message.

Their value means nothing to users, so qdev_print_props() shouldn't
print it.  Fix by removing their print method.

Their only use is dirty hacks.  Document that.

Users can't create them, so qdev_device_help() shouldn't list them.
Fix that.

Also make qdev_device_add() pretend they don't exist.  Before, it
rejected them with a "can't be added via command line" message, which
wasn't quite right for monitor command device_add.

To make it obvious that -device and device_add can't die in
hw_error().

"device_add isa-serial,bus=pci.0" kills QEMU.  Not good.

New LOC_CMDLINE.  Use it for tracking option with argument in
lookup_opt().  We now report errors like this

    qemu: -device smbus-eeprom: Did not find I2C bus for smbus-eeprom

New LOC_FILE.  Use it for tracking file name and line number in
qemu_config_parse().  We now report errors like

    qemu:foo.conf:42: Did not find I2C bus for smbus-eeprom

In particular, gems like this message:

    -device: no driver specified

become almost nice now:

    qemu:foo.conf:44: -device: no driver specified

(A later commit will get rid of the bogus -device:)

New struct Location holds a location.  So far, the only location is
LOC_NONE, so this doesn't do anything useful yet.

Passing the current location all over the place would be too
cumbersome.  Hide it away in static cur_loc instead, and provide
accessors.  Print it in error_report().

Store it in QError, and print it in qerror_print().

Store it in QemuOpt, for use by qemu_opts_foreach().  This makes
error_report() do the right thing when it runs within
qemu_opts_foreach().

We may still have to store it in other data structures holding user
input for better error messages.  Left for another day.

error_report() terminates the message with a newline.  Strip it it
from its arguments.

This fixes a few error messages lacking a newline:
net_handle_fd_param()'s "No file descriptor named %s found", and
tap_open()'s "vnet_hdr=1 requested, but no kernel support for
IFF_VNET_HDR available" (all three versions).

There's one place that passes arguments without newlines
intentionally: load_vmstate().  Fix it up.

Commit 30d335d6 converted an informational message from
monitor_printf() to qemu_error(), probably because the latter doesn't
need a mon argument.  A later commit will make qemu_error() print
additional stuff that is only appropriate for proper errors, and then
this will break.  Clean it up.

qbus_find() adds an informational line to error messages, and prints
both lines with one qemu_error().  Use error_printf() for the
informational line instead.

While there, simplify: instead of printing buffers filled by
qbus_list_bus() and qbus_list_dev() in one go, make them print it.

qdev_device_help() prints device information with qemu_error().  A
later commit will make qemu_error() print additional stuff that is
only appropriate for proper errors, and then this will break.  Use
error_printf() instead.

While there, simplify: instead of printing a buffer filled by
qdev_print_devinfo() in one go, make qdev_print_devinfo() print it.