add pure perl code to allow backends like jvm and moar

When this dist is installed via panda, it will choose the parrot specific code
on parrot only, and will fall back to the pure perl version.
In case Build.pm is not supported (e.g. installation without panda) it will
use the pure perl version in all cases.
s/constant/my \\/ because of a precomp bug
Merge pull request #4 from FROGGS/master

[add pure perl code to allow backends like jvm and moar.]

That is really cool.