Try without shallow clone if fatal error

Previously, it was only considered a shallow failure if the error details matched `/rpc failed/i` (see #744, #747).  Here's what a shallow failure looks like for me:

    $ git --version
    git version 1.7.12.4

    $ git clone https://code.google.com/p/closure-library -b master --progress . --depth 1
    Cloning into '.'...
    fatal: expected shallow/unshallow, got Error: internal server error