[Therion] cs suggestion: Outside bounds warning

[Andrew Atkinson]

Hello

A strange rotation was encountered relative to the grid, when playing with
cs OSGB:SN
and
cs EPSG:27700

In the end this was tracked down to the fact that the 300000 400000, was 
still within all the fixes, which is wrong, but this put it well outside 
the SN area, and hence the rotation. (or that is what we think)

Which lead me to the thought, maybe therion should warn, but continue if 
it finds an co-ordinate outside the area covered by the cs selected?

Not sure if this is possible (easy) to do, but in this case would have 
saved lots of head scratching.

Andrew