Should set_analysis report on the "new" filter expression?

[DougBurke]

Once #1562 lands we have

In [1]: from sherpa.astro.ui import *
WARNING: imaging routines will not be available, 
failed to import sherpa.image.ds9_backend due to 
'RuntimeErr: DS9Win unusable: Could not find ds9 on your PATH'
WARNING: failed to import sherpa.astro.xspec; XSPEC models will not be available

In [2]: load_pha("3c273.pi")
WARNING: systematic errors were not found in file '3c273.pi'
statistical errors were found in file '3c273.pi' 
but not used; to use them, re-read with use_errors=True
read ARF file 3c273.arf
read RMF file 3c273.rmf
WARNING: systematic errors were not found in file '3c273_bg.pi'
statistical errors were found in file '3c273_bg.pi' 
but not used; to use them, re-read with use_errors=True
read background file 3c273_bg.pi

In [3]: ignore(hi=0.5)
dataset 1: 0.00146:14.9504 -> 0.5694:14.9504 Energy (keV)

In [4]: ignore(lo=7)
dataset 1: 0.5694:14.9504 -> 0.5694:6.57 Energy (keV)

In [5]: ungroup()

In [6]: get_filter()
Out[6]: '0.569400012493:6.570000171661'

In [7]: notice()
dataset 1: 0.5694:6.57 -> 0.00146:14.9504 Energy (keV)

In [8]: ignore(hi=0.5)
dataset 1: 0.00146:14.9504 -> 0.511:14.9504 Energy (keV)

In [9]: ignore(lo=7)
dataset 1: 0.511:14.9504 -> 0.511:6.9934 Energy (keV)

In [10]: group_counts(20, tabStops=~get_data().get_mask())

In [11]: get_filter()
Out[11]: '0.510999977589:6.993400096893'

In [12]: set_analysis("wave")

In [13]: get_filter()
Out[13]: '1.772874219724:24.263051435945'

In [14]: set_analysis("chan")

In [15]: get_filter()
Out[15]: '36:479'

There is an argument to be made that set_anaysis and the groupXXX commands could report new filters in the same way that notice and ignore now do. Note that groupXXX commands now report the filter as #1637 has landed

We have a similar issue with set_coord, but there it is a bit-more serious, but we recently changed things so the spatial filter gets cleared:

In [16]: clean()

In [17]: load_image("acisf08478_000N001_r0043_regevt3_srcimg.fits")

In [18]: set_coord("physical")

In [19]: notice2d("circle(4324.5,3827.5,430)")
dataset 1: Field() -> Circle(4324.5,3827.5,430)

In [20]: set_coord("logical")
WARNING: Region filter has been removed from 'acisf08478_000N001_r0043_regevt3_srcimg.fits'

This is only for the UI level, not the lower-level Data methods.