Add $PREFIX to pkg command
Add "is pkg used" check
Simplify return code handling
Minor improvements
Rename 460.chkpkgsum to 460.pkg-checksum for uniformity
Fix bunch of typo and copy/paste mistakes. Remove redundant comments
Merge remote-tracking branch 'origin/master' into periodic
Enhance plugins management in main().

If a command is not found, when falling-back to plugins, display usage
only if no plugin corresponding to the requested command exist.  If such
a plugin exist and returns an error, do not display usage.

While here remove an inappropriate "not reached" comment on a reached
return.

Fixes this behaviour:
~~~
% pkg Hello World && echo OK
OK
%
~~~
Attempt to display a manual page for plugins

Try do display the pkg-plugin man page.  If it's not available, this
result in:

~~~
% pkg help plugin
No manual entry for pkg-plugin
~~~

which is still better than:

~~~
% pkg help plugin
pkg: 'plugin' is not a valid command.

See 'pkg help' for more information on the commands.
~~~

if such a plugin is available...
Merge pull request #428 from aklv/periodic

Improvements to periodic scripts.
Merge pull request #434 from smortex/warn-invalid-commands

Enhance plugins management in main().
Merge pull request #436 from smortex/plugins-help

Attempt to display a manual page for plugins
add -l flag in usage string, it was already in pkg(8) man page

Conflicts:
	pkg/main.c
add pkg-convert(8) man page and update zsh completion
error message when repo abi mismatch miss a space
Fix error in humanize_number() call.  On master this seems not to
cause a problem, but on release-1.0 this least to 'pkg stats' failing
an assertion an dumping core.
Fix build error due to size being int64_t
Remove trailing whitespace
Start sentence on newline
Update my address and direct users to pkg@FreeBSD.org