BPyMessages - added "Save over" message for scripts to use, so as not to overwrite files.

import_obj - comments, docstring additions, cleanup.

OBJ export: -renamed export_obj
 faster edge exporting (use edges LOOSE flag rather then finding zero face user edges)
 check for file before overwriting
 use object iterators

release/scripts/bpymodules/BPyMessages.py

@@ -1,4 +1,4 @@
-from Blender import Draw
+from Blender import Draw, sys
 def Error_NoMeshSelected():
 	Draw.PupMenu('ERROR%t|No mesh objects selected')
 def Error_NoMeshActive():
@@ -8,3 +8,11 @@ def Error_NoMeshUvSelected():
 def Error_NoMeshUvActive():
 	Draw.PupMenu('ERROR%t|Active object is not a mesh with texface')
 
+def Warning_SaveOver(path):
+	'''Returns - True to save, False dont save'''
+	if sys.exists(sys.expandpath(path)):
+		ret= Draw.PupMenu('Save over%t|' + path)
+		if ret == -1:
+			return False
+	
+	return True