print_conflicting_files from bee update to slow for big archives

[donald]

sudo bee update libxcb takes forever ( = longer, that I ever had the patience to wait ). The package
libxcb contains 10908 files. In print_conflicts() from /usr/libexec/bee/bee.d/bee-cache, print_conflicting_files "${pkg}" | cut -d ' ' -f8- | sed -e 's,.*, &$,' build a list of 8249 patterns, which are applied to the output of tmp_merge_install_inventory_files "${TMPINSTALL[@]}" which contains 339184 files. With the 8249 patterns, the grep will spit out about 10 lines a seconds, so my estimate for that step alone is about 15 minutes, but I'm sure I waited longer for bee update to complete. @pmenzel said, it took about an hour.

When print_conflicts is disabled, the bee update takes no time at all.

As a side note, the patterns generated from the filenames are not escaped and filenames containing pattern metacharacters ( e.g. /usr/bin/[ ) might have unexpected consequences.