Add support to detect arm vs armv6

There are two different versions of the ARM ABI depending on the
TARGET_ARCH. As these are sligntly different a package built for one
may not work on another. We need to detect which one we are on by
parsing the .ARM.attributes section.

This will only work on the ARM EABI as this section is part of the ABI
definition. As armv6 only supports the ARM EABI this is not a problem
for the oabi.

Older versions of libelf in FreeBSD fail to read the .ARM.attributes
section needed. As armv6 is unsupported on these versions we can assume
we are running on arm.
Merge pull request #581 from zxombie/master

Add support to detect arm vs armv6
Use tokeniser from libedit to convert a string to argv

Remove the unclean str2argv
Remove stray reference to the -X option, which was removed months ago.

Fixes #586
Turn REPOS_DIR into a list or repository to read configuration from

By default read configuration from /etc/pkg and /usr/local/etc/pkg/repos

Discussed with:	jonathan, des, gavin (@BSDCam)
Allow to overwrite repository configure

This allows to disable a repository configured in base from a localbase
configuration file (convenient for RO base)
Deprecate packagesite
Introduce a new "fingerprint" type of signature

Discussed with:	jonathan, des, gavin (@BSDCam)
Add a function to compute a sha256 hash out of a buffer
Allow to check rsa from buffer
New fingerprint kind of signature

if a repository is declared using the fingerprint type of signature.
a fingerprint directory should also be provided. Inside that fingerprint
directory should be found 2 directories trusted and revoked.
Those directories will contains files (in yaml format) containing the
fingerprint of the trusted certificated and the revoked ones:

--- begins --
function: sha256
fingerprint: an_hex_representation_of_the_fingerprint
--- ends ---

All unknown attribute will be silently ignored to allow extending in the
futur

It also support multiple signatures inside the catalog. the catalog
should provide the signature in the following form:
name.sig
name.cert

Discussed at:	BSDCam
Discussed with:	des, jonathan, gavin
Fix spelling

Reported by:	matthew
pkg.8: Update example for detecting pkg(8) to support pkg-devel

Reported by:	Takanori Saneto <sanewo@ba2.so-net.ne.jp> (ports/181813)
Make sure the default configuration is without any signature
Fix syslog badly reporting reinstallations
Fix memory leak in pkg-repo.

Free memory when we do not add a package to the resulting site for
some reason.