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toggle val type: "valn:" vs. "valup:" (native vs. upsample)
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keyboard equiv: <none>

This entry has two different states, "valn:"
(real or complex valued, *native* resolution) and
"valup:" (real or complex valued, *upsampled* to
structural resolution).

On startup, the default stat is "valn:", which is
used to (re-)read ("R" button) native-resolution
stats (bfloat or float BRIK format), register
them to the structural underlay, and upsample to
structural resolution.  This are the same steps
performed by the VOLUME-STATS button on the csurf
SessionTools -> View Functional Data panel.

Clicking on the label "valn:" (bold to indicate
it is button-like) swaps in the "valup:" entry,
which is used to read ("R" button) *and* write
("W" button) already-registered and
upsampled-to-structural (1mm^3 or 0.5mm^3)
resolution stats (float BRIKs only).  Note that
these are considerably larger files than the
native stats (64M for 1mm^3), but compress well.

Clicking again toggles back to "valn:"
