Clean.sh: No need for realpath(1)
Clean.sh: Remove redundant check on clean_rdepends
Clean.sh: Speedup skipping by avoiding redundant recusive cleanups.

This works by removing all rdep references when a pkg is removed from
/deps due to being skipped. The old code would still keep looking
at all rdeps and continually try to remove the same packages
over and over again.
compute_deps: Speedup 9% by using :> instead of touch
Use case instead of [] for checking empty dir as it is slightly faster.

$ rm -rf dir; mkdir dir; for n in $(jot 24000); do :> dir/${n}; done
$ /usr/bin/time sh -c 'for n in dir/*; do :; done;'
        0.04 real         0.03 user         0.01 sys
$ /usr/bin/time sh -c 'for n in dir/*; do [ "${n}" = "${n}/*" ] && break; :; done;'
        0.09 real         0.08 user         0.01 sys
$ /usr/bin/time sh -c 'for n in dir/*; do case "$n" in "dir/*") break ;; esac; :; done;'
        0.05 real         0.03 user         0.02 sys

Suggested by:	jilles
Remove redundant cleanup
Fix crashed build detection in deadlock_detected()

MFH