compress: improve & fix recursive mode
compress: improve & fix recursive mode

The 4.2 version broke the exit status when running in recursive
mode and some files were skipped due to already being compressed
or decompressed.  While we fix that, also address the UI that the
4.1 version (which added recursive mode) documented: we simply do
not warn if files are already compressed/decompressed.

valgur/ncompress,valgur/ncompress