add support for following symlinks

[anarcat]

I am a user of git-annex which makes heavy use of symlinks to store large files. A gdu of my Photos disk looks like this:

 gdu ~ Use arrow keys to navigate, press ? for help                                                                                                          
 --- /media/sda3/Photos ---
                         /..                   
  487.1 GiB [######### ] /.git
   73.2 MiB [          ] /2018
   58.6 MiB [          ] /2019
[...]

... while ncdu -L (since 1.14) can provide a more accurate view:

ncdu 1.17 ~ Use the arrow keys to navigate, press ? for help
--- /media/sda3/Photos --------------------------------------------------------------------------------------------------------------------------------------
                                     /..
  487,1 GiB [######################] /.git
  153,3 GiB [######                ] /2018
  118,3 GiB [#####                 ] /2019

Of course, it double-counts the files then:

--- /media/sda3 ---------------------------------------------------------------------------------------------------------------------------------------------
        0,9 TiB [######################] /Photos

... instead of the more logical:

--- /media/sda3 ---------------------------------------------------------------------------------------------------------------------------------------------
  489,3 GiB [######################] /Photos

... but I'm fine with that, as that's to be expected. The patch for ncdu might be an inspiration for you, simple and easy...

let me know if you want one for gdu, i might be able to figure something out, even though i never peeked at the code so far.