Some improvements on the fix of 4399 GUI: Exclude directory with absolute path does not work

Improve the fix for ticket 4399 ('C:foo\bar\' is no more regarded as an
absolute path) and add few tests

Ticket 4399# Windows accepts both '\' and '/' as folder separator so let's handle them
both.

Fix silly compilation error

Update Makefile with dmake for the fix of 4399

Fix 'lets-assume-that-the-mask-is-a-subfolder' problem and other issues commented by Daniel

Add test for Path::getCurrentPath()

Let's don't do the search twice

Make size_t const