Fixed cache warmup of paths which contain back-slashes:

At this step in the warmup process there is a string replacement made, but paths with backslashes
are written into the cache file as something like `C:\\path\\to\\cache/pro_/...` but the str_replace
searches for the plain string `C:\path\to\cache/pro_/...`, which produces no matches.

The fix solves this by using var_export to escape the search (and replace) paths so they match the
format originally output into the cache file.