SetMagIndex
   calls AssessMagISchange  which sets transIS
   calls AssessRestoreIS  which overlays its own transIS
   After the mag change, if either of these said to do it, it gets
   the axisIS, subtracts from the transIS and sets image shift

AssessMagISchange: given from and to mag, computes delIS from change in
neutral IS and offsetIS which is 0 if not applying (real offset stored in
calOffsetIS)
Sets flag to convert if both LM or nonLM, apply is on, or low dose mode
Then if that is set or there is a nonzero result or mag change resets IS,
it gets the current image shift and computes the AxisIS
if converting, it adds back axisIS and subtracts its neutral/offset components
to get the raw plus tilt axis offset if shifting to axis, called a "real"
shift.  This is transferred to the new mag and the CHANGE is added to the delIS
The newIS is a raw value which is the old raw value plus this delta, and will
need to be adjusted by new AxisIS
It is applied if (nonzero or mag change resets IS) AND (staying in LM/M,
applying offset, or in low dose mode)  [Low dose added 2749]

GetImageShift gets raw IS and subtracts current TiltAxisIS

GetTiltAxisIS works off the last mag index:
Starts with neutralIS + offsetIS  (in JEOL EFTEM it explicitly bases this on
neutral index in case of switching)
Adds in the tilt axis offset converted to IS at this mag if shifting to axis

SaveOrRestoreIS happens for JEOL going (from nonLM to diff) or (from LM to diff
if applying offset) or if going between LM/nonLM and not applying offset and
not low dose mode (latter in Jan 2018).
Otherwise (noJEOL) it only happens going to diffraction from any mag AND
applying offsets
WTF?

SaveISifNeeded checks whether it is supposed to save, and gets the IS and
adds on the axisIS to get the rawIS to save.

AssessRestoreIS checks whether there is supposed to be a restore and there
is a saved IS
From the rawIS it subtracts neutralIS and offsetIS to get real IS at saved mag
This is transferred to the new mag and neutralIS and offsetIS added back on to
get new raw IS to apply at new mag

Low dose:
Search mode history:
2749 initial: Low dose added to AssessMagISchange, only split beam shift dealt
with
2943, PLA before leaving search not after
2966: fixed for search on JEOL: also do it later if PLA and going to search

Initially added low dose to the
Do IS at higher mag for consistency in beam shifts, BUT original logic was to
do PLA AFTER IF going to focus/trial from another area
Does IS first if:
1) When using PLA and either going between F/T and not, or coming to or from
search:
 do it if coming from focus/trial or search
2) Otherwise: do it first in two cases:
  a) (Going to DIFF or to a lower mag and NOT entering low mag) or I added
     leaving low mag!
  b) Staying at same mag index and increasing alpha!

So if doing it first it calls DoISforLowDoseArea which makes the net change
Then it changes mag
Then does the IS change if doing after.

DoISforLowDoseArea 
convert image shift at new area to the current mag into delIS
converting image shift at current area to current mag, subytract from delIS
Apply delIS

OK: why not just compute the delIS at the new mag after you know what it is,
applying it if is the same mag or STEM mode OR
telling AssessMagISchange what it is which it will add on if mChangingLDArea
is set
And the reason this won't work is that THIS change involves beam shift!

Split beam shift if either leaving low mag from known area or entering low
mag from known or unknown area
Which means it pulls off beam shift of curren area before changing mag and
afterwards, it applies the full image shift instead of a change
All this stuff can stay the same is it is complicated by probe mode
Really just want it to find out what beam shift accompanies the image shift
and add it to the final beam shift.
Also, theoretically the image shift to align V or S should not be accompanied
by a beam shift, just the IS involved in going to or from T/F/R
Is balanced shift applied to V also?