Add new option destroot.keepdirs to eliminate need for .turd files

[jberry@…]

Patch file attached.

.turd files have traditionally been used to prevent empty directories that are actually needed, from being deleted during the destroot phase. But .turd files are ugly, and cause a variety of ugly complications as well.

The attached patch adds a new option destroot.keepdirs which accepts a list of paths in destroot that should be "kept".

The implementation simply adds additional options to the find command which searches for empty directories, in order to exclude these "keepdirs" from the search.

The directories to keep are specified by full paths into the destroot. My only question on this patch is whether specifying these as destroot paths is appropriate, or whether they should be specified relative to prefix.

[jberry@…]

Patch to base/src/port1.0/portdestroot.tcl