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.
