CSV export in columns, math channel iterator fix

[dendvz]

1. CSV export into long lines looks pretty useless, e.g. they make LibreOffice Calc fail with message "The data could not be loaded completely because the maximum number of columns per sheet was exceeded". Changed CSV export to columns. X-axis (time/frequency) values are printed in each line, thus making import into plot tools easier.
2. Fixed bug in MATH channel (double-increment of iterator), changed postfix iterator increments to prefix increments.
3. Improved DSO6022BE Software trigger stability by increasing dropped sample count to 1040 (0x410). Most likely the same buffer truncation needs to be applied to 6022BL. Still have to dive into jhoenicke's firmware, fast sample rates might require different approach to data acquisition.

[davidgraeff]

Could you please squash the pull request to one commit? Command line:
git rebase -i HEAD~20
And follow the instructions.

[dendvz]

Squashed commits as requested.

[davidgraeff]

I reviewed the code and 2. and 3. looks good to me.
For 1.: Can you add a generated csv file here in the comments area, so that I can see the effect of your changes? @dendvz

[dendvz]

before.csv and after.csv renamed into *.txt.
before.txt
after.txt

LibreOffice Calc error message:

[davidgraeff]

Thanks, LGTM