inconsistent load* opcodes

[Will Coleda]

.sub mariner
$P1 = loadlib 'chud'
say "ok 1"
load_bytecode 'chud'
say "ok 2"
.end

Suggestion:

1) make the $P1 optional on the loadlib - most of the example usages
for loadlib ignore the returned PMC status. (Keep that variant as
it's need for dlfunc, etc.)
2) make loadlib throw an exception when it can't load the library.
(defaulting to on, configurable via errors*)
3) rename loadlib to load_library

Thoughts?