MNT: reduce at limit error to warning

[ZLLentz]

Prospective fix for @ghalym 's reported slits motion issues.

The code prior to this PR raises an error if we are:

• At a limit switch
• We try to move past the switch

Because the user should be told of this so they know why the stage didn't move.

However, the consequence of making it an error is that this will lock up the motion until the error is acknowledged and cleared. This means that automation routines (even just "move the slit blades together" routines) need to know to clear errors to make them work reliably, and then we run a risk of automatically clearing other error types that might be more serious. In practice now, this may lead to the state where we ask for the slits to open twice, then some axes get stuck at a limit, so asking the slits to close causes not all the blades to close.

Since this status is not dangerous to anyone or anything, this PR reduces it to a warning. A warning:

• Uses the same error text field as the errors
• Does not bring the axis into a MAJOR/MINOR alarm state
• Does not flip bError to TRUE
• Does not provide an error code
• Will clear itself automatically at the next successful move

This can be read clearly in the screen for the user to know why a motion did not begin, but does not lend risks to automation routines.

[ZLLentz]

I had the same thought Ken. Perhaps the clean way to do this is to add new bWarning and nWarningID variables, and rename sErrorMessage to sStatusMessage. Then it can be very clear what is going on.

[ZLLentz]

I have made an issue for doing this better in a future PR. I will merge this and see if there is any low-hanging-fruit to tackle before tagging.