Add conversion of case insensitive input to real path

[olabetskyi]

On windows we can accept case insensitive file names but cppcheck can't work with those> so we have issue like this:

C:\Users\danielm\cppcheck>c:\Users\danielm\run-cppcheck\run-cppcheck.exe "c:\Users\danielm\cppcheck\cli\main.cpp"
cppcheck: error: could not find any files matching the filter.

Because the real name of the disk is C and not c
Solution: add conversion of the file path to real path.