Absolute/Relative paths fix

This fix the absolute/relative path issue. I have added new css files to
the test website in order to allow you to reproduce the bug (independent
PR)
Added more css files to the test website in order to reproduce bugs

2 bugs:
- Absolute relative path: without the fix I have submitted some minutes
ago, the second div will not display the background image (file
css-style5.css) because this file is imported from a file that it is in
the same directory.
- Cache dependencies don't work properly: To reproduce the error, load
the test web page, after modify the file css-style3.css, after modify
the file css-style4.css, and again the file css-style3.css and you will
see that cruncher is not detecting the change and doesn't create a new
version. As far as I had time to investigate, it seems there is a bug in
the file cache dependencies (file monitors).
Optimisation regarding the new "Physical files" feature

We have detected that with the new feature, an I/O operation is going to
be performed for every request. For a very busy site could be be
thousands of requests per minute, which means thousands of I/O
operations.
This optimization reduces the I/O operations to 1 per minute (for any
resource that has been previously cached and crunched)
Merge pull request #18 from Alain-es/dev

Absolute/Relative paths fix