Uniform syntax for enums should be implemented

[brycelelbach]

[reported by blelbach] [Trac time Wed Aug 10 15:30:33 2011] Currently, some of our older enums (such as the one for thread state, and error
codes) use a different syntax than our newer enums. Our newer enums always
prefix the enum name, e.g.

    enum foo {
        foo_bar,
        foo_buzz
    };

Our older enums generally take the form of:

    enum foo_enum {
        bar,
        buzz,
    };

We should pick a style, bite the bullet and update all the enums to that style.

[hkaiser]

This is a major breaking change, its too late in the release cycle to fix this

[hkaiser]

I think this can be closed now as the Boost scoped enum emulation has been replaced by C++11 strongly typed enums (see #2050).