option to ignore missing layers at run-time

[pkishor@…]

If a layer defined in the mapfile doesn't exist on the hard-disk, MapServer throws an exception. 
This can be disabled by configuring "-DIGNORE_MISSING_DATA" at compile time. It would be 
useful to have this as an option switchable during run-time so that MapServer (and MapScript) can 
be made to work under strict or tolerant mode.

[sdlime]

It's a good idea, should be easy to add too. I'd propose adding a LAYER level 
flag

[sdlime]

Whoops, this form is a bit sensitive. As I was saying. I'd propose adding a 
LAYER level attribute to control this. For some upcoming work I've got here I'd 
like that level of control. The alternative would be something at the MAP level 
but layerObj's persist all the way to the shapefile opening code (I think) and 
may be the better spot. Anyway, I'll have a look...