Refactor to reduce dependancy on ios.c

Rationale:

    Unravel ios.c’s legacy role as debug io library for the runtime;
    vs current role as backend for iostream.jl.

Clean up historical debug printf functions:

    Replace calls to ios_printf(), ios_puts(), JL_PRINTF, JL_PUTS etc
    with jl_printf(), jl_puts()...

Remove ios.c dependance from ast.c and builtins.c:

    src/flisp/flisp.c:

        New fl_load_system_image_str(char*, size_t)
        Hides detail of ios_static_buffer from ast.c
        ios_* no longer used in ast.c.

    src/builtins.c

        In jl_errorf(), replace ios_vprintf() with vasprintf()
        (following the precedent set by src/jl_uv.c:663).

Use free() not LLT_FREE() to clean up after vasprintf() in jl_uv.c:

    man vasprintf says “asprintf() and vasprintf() dynamically
                        allocate a new string with malloc(3)”

Dead code removal:

    jl_uv.c: jl_bufptr(), jl_ios_buf_base()
    sys.c: jl_ios_size()
Merge branch 'master' of octech.github.com:samoconnor/julia
Handle early errors.

Use fputs() in place of jl_printf() in jl_errorf()
in case JL_STDERR is not yet initialised.

Initialise JL_STD* as soon as jl_io_loop is available.