Clean up the string functions

Avoid two evaluations of src in util_strpcpy clean the code in the ones
where the pointer passed is not modified and merge the main loop of
util_strpcpyl and util_strscpyl into util_strpcpyv.  Also make strpcpy
more compact by removing some unnecessary arithmetic.

Cleanup util_strpcpyv by shortcutting size == 0 case

Do some style fixups

Signed-off-by: Ian Stakenvicius <axs@gentoo.org>
Fix buffer overflow

Signed-off-by: Ian Stakenvicius <axs@gentoo.org>
Respect the MIT license

Signed-off-by: Ian Stakenvicius <axs@gentoo.org>