Update and rename overlay-diff to overdiff

Use the PORTAGE_TREE environment variable as location of the Portage
tree. Default to /usr/portage if unset or null.
Update dev-util/gource-0.42

Fix invalid atom dev-libs/pcre:3 in DEPEND: should be dev-libs/libpcre:3

Package-Manager: portage-2.2.8-r1