@diff.tree - show file differences between 2 directories

   Given: 2 directory names

   If desired, list files that do not exist in one of the directories.
   For the files that exist in both directories, list those that differ.
   If desired, show the actual differences.

   This is similar to @diff.files, which only looks at files in a
   specified list.

usage: @diff.tree [OPTIONS] new_dir old_dir"


   -diff_opts 'OPTS'      : apply OPTS as options in diff commands
   -ignore_append i1 ...  : append to ignore_list (list in quotes)
   -ia                    : short for -ignore_append
   -ignore_list i1 ...    : create new ignore_list (list in quotes)
   -il                    : short for -ignore_list
   -ignore_missing        : only compare overlapping files
                            If different files, fail.
   -no_diffs              : only compare existence of files
   -quiet                 : only list files with diffs
   -save                  : save actual file differences (txt and pdf)
   -show                  : show actual file differences
   -show_list_comp        : show any pairwise differences in file lists
                            (terminate after showing comparison)
   -skip_data             : skip binary diff of select data files
                            (.BRIK, .dcm, .BRIK.gz)
   -verb LEVEL            : set verbosity level (0,1,2)
                            (default 1)
   -diff_prog PROG        : use PROG to show diffs (e.g. xxdiff, meld)
   -xxdiff                : use xxdiff to show diffs
   -X                     : implies -xxdiff -ignore_missing


     @diff.tree here/this.dir ../../../there/that.dir
     @diff.tree -show_list_comp test1/FT/SUMA test2/FT/SUMA

R Reynolds    written ages ago, but added 10 Jun, 2015