Pull in new slots when appropriate, bug #478188.
emerge: accept --pkg-format option

Accept --pkg-format option which will override settings of
PORTAGE_BINPKG_FORMAT. Currently takes choices of 'tar' (original gentoo
binary package), 'rpm' or its combinations.

Signed-off-by: Tomáš Čech <sleep_walker@suse.cz>
Exclude PORTAGE_BINPKG_FORMAT from ebuild env.
_want_update_pkg: respect --exclude
dep_zapdeps: skip want_update_pkg if pkg in graph
man: Cap lines at 80 chars
man: Remove trailing spaces
install.py: split out optparse compat code
install.py: handle zero file arguments (--help)
bin/fixpackages: Add -h, fixes bug #394773
man/emerge.1: Mention slots for bug #424930
man/emerge.1: Fix bug #405783 by elaborating -n
man/emerge.1: Mention log files, fixes bug #462802