Workaround libarchive no 100% supporting mtree (doesn't know nocache)
Removed unused pkg_open from pkg add

Conflicts:
	pkg/add.c
prepend multirepos by repo- this avoid having the need to get reserved names (fixes #394)
If mirror is stored in http use If-Modified-Since (fixes #425)
No need to check the scheme to chose the right method, libfetch does it already
Register the packagesite in repository metadata, if it has changed refetch the
metadata

Fixes:		#426
Reported by:	swills
Fix output of `pkg check -s`.

Due to a lacking break, `pkg` output:

pkg-1.0.6: checksum mismatch for /usr/local/lib/libpkg.a
pkg: : /usr/local/lib/libpkg.a(f218119bf90cfda565a798efa772210e564397d623772de67149523cfe4a7ab6): Unknown error: -46
pkg-1.0.6: checksum mismatch for /usr/local/sbin/pkg
pkg: : /usr/local/sbin/pkg(8d2b9ff7309d0be85962a7de9406157735d9c0bce4592aabc00a9c8e34452abd): Unknown error: -14144
pkg-1.0.6: checksum mismatch for /usr/local/sbin/pkg-static
pkg: : /usr/local/sbin/pkg-static(cf9ef62ad4235fa5f6d461c1ac7a87292e4c0c3dec5f915ded83d0d1568c8175): Unknown error: -14144

instead of:

pkg-1.0.6: checksum mismatch for /usr/local/lib/libpkg.a
pkg-1.0.6: checksum mismatch for /usr/local/sbin/pkg
pkg-1.0.6: checksum mismatch for /usr/local/sbin/pkg-static

Conflicts:
	pkg/event.c
Use _PATH_BSHELL instead of /bin/sh