build.py: loaderString should escape \-characters?

I have almost no experience in python, but I think loaderString should escape backslash-charaters.

I dit a quick test with a file  with 3 lines, where the first and last line are empty and the middle line contained the string "\n".

When importing this file with @@INCLUDESTRING:@@ the generated file contained the string "\n\n\n", which is obviously wrong, because that would be 4 empty lines. After adding the .replace('\\', '\\\\') the string was "\n\\n\n" which should be the correct behaviour in my opinion.