Add wrapper for seek() on posixy systems.
Add boolean 'strhas()' function.
API change: strsplit("") -> [][:]

    Splitting an empty string now gives am empty list, instead
    of a list with a single empty string. Seems more intuitive.
Actually add the seek code.
Remove dial.myr in favor of platform specific ones.

    we have dial+posixy.myr and dial+plan9.myr
Same with resolve.myr: resolve+plan9.myr and resolve+posixy.myr
Also env vars: env.myr gone in favor of env+plan9.myr, env+posixy.myr