compiler: deref receiver types in mangled names

compiler: deref receiver types in mangled names

    This was the original intent, as reflected in the long comment at the
    start of names.cc, but I forgot to implement it.

    Also, remove a leading ".0" from the final name.  That could occur for
    a method whose receiver type starts with 'u', as in that case we
    prepend a space to the mangled name, to avoid confusion with the
    Unicode mangling, and the space turns into ".0".

    Also, if the Unicode encoding would cause the final to start with
    "..u" or "..U", add a leading underscore.

    Patch gotest to not get fooled by some names.

    The result of these changes is that all symbols start with a letter or
    an underscore.

    Reviewed-on: https://go-review.googlesource.com/90015

From-SVN: r257068