cutils: Make strtosz & friends leave follow set to callers

strtosz() & friends require the size to be at the end of the string,
or be followed by whitespace or ','.  I find this surprising, because
the name suggests it works like strtol().

The check simplifies callers that accept exactly that follow set
slightly.  No such callers exist.

The check is redundant for callers that accept a smaller follow set,
and thus need to check themselves anyway.  Right now, this is the case
for all but one caller.  All of them neglected to check, or checked
incorrectly, but the previous few commits fixed them up.

Finally, the check is problematic for callers that accept a larger
follow set.  This is the case in monitor_parse_command().
Fortunately, the problems there are relatively harmless.

monitor_parse_command() uses strtosz() for argument type 'o'.  When
the last argument is of type 'o', a trailing ',' is diagnosed
differently than other trailing junk:

    (qemu) migrate_set_speed 1x
    invalid size
    (qemu) migrate_set_speed 1,
    migrate_set_speed: extraneous characters at the end of line

A related inconsistency exists with non-last arguments.  No such
command exists, but let's use memsave to explore the inconsistency.

The monitor permits, but does not require whitespace between
arguments.  For instance, "memsave (1-1)1024foo" is parsed as command
memsave with three arguments 0, 1024 and "foo".  Yes, this is daft,
but at least it's consistently daft.

If I change memsave's second argument from 'i' to 'o', then "memsave
(1-1)1foo" is rejected, because the size is followed by an 'f'.  But
"memsave (1-1)1," is still accepted, and duly saves to file ",".

We don't have any users of strtosz that profit from the check.  In the
users we have, it appears to encourage sloppy error checking, or gets
in the way.  Drop the bothersome check.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
