[Mapscript-PHP] layer->open shouldn't produce a fatal php error.

[zjames@…]

The function $layer->open() currently causes a fatal php error when there is any failure in opening the 
layer. Since this terminates the instance of php opening the layer, it's difficult for php applications to 
recover cleanly. If this fatal error was downgraded to a php warning, interactive applications could test 
layers to see if they were correctly configured and provide feedback to the user.

[dmorissette]

Done in 4.3 CVS (php_mapscript.c rev 1.201)