ols: Don't reduce sample count just because it's not a multiple of 4.
scpi: Log responses received by sr_scpi_get_string().
rigol-ds: Use common rigol_ds_config_set() function throughout.
rigol-ds: Overhaul VS5000 and DS1000 support.

This change moves the handling of series differences out to the points in the
code where they actually matter, unifying the overall structure of the code.

It also adds new VS5000/DS1000 series equivalents for commands that were
previously only implemented on the later models.

After this change, trigger waiting and the 'Memory' data source are supported
on the VS5000/DS1000 series.
rigol-ds: Overhaul vendor/series/model info and protocol variants.
scpi_usbtmc: Improve debugging output.
rigol-ds: Only protocol v3 adds trailing linefeeds to data blocks.
rigol-ds: Improve protocol debugging output, abort on read errors.
rigol-ds: Stop capture cleanly on read errors.
rigol-ds: Fix divide by zero when no analog probes selected.
scpi_serial: Reimplement to allow scpi_read_complete() to work correctly.
rigol-ds: Fix partial read handling in header parser.
rigol-ds: Don't run rigol_ds_block_wait() code unless supported.
sysclk-lwla: Advertise SR_CONF_CONN option.
sysclk-lwla: Do not reset drv_context.instances on scan.

Apparently, frontends may call scan() more than once to accumulate
multiple devices, so do not reset the instance list pointer at the
start of each scan.  Also, number devices continuously across scans.
sysclk-lwla: Implement config_probe_set() callback.

Move setup of channels and trigger masks to the new probe
configuration callback.  Although the actual hardware setup
still happens just before acquisition, the new approach
already has the advantage that invalid settings are caught
early.
Also, it turns out that the LWLA1034 allows triggering on
channels which are not enabled for data acquisition.  This
feature is now supported as well.
sysclk-lwla: Implement config_commit() callback.

Move pre-acquisition hardware setup to the new config_commit()
callback.  At the moment, the only setting applied at commit
time is switching the clock source, which involves uploading
a new bitstream to the FPGA.
rigol-ds: Fix a couple of compile warnings.