Previously, piglit_get_gl_version() had three return values: the GL
version (major and minor version numbers separately) and a boolean
indicating whether or not the API is GL ES.  This meant that we had to
jump through hoops in order to use it, e.g.:

    /* Are we using GL with a version of at least 3.1? */
    bool es;
    int major;
    int minor;
    piglit_get_gl_version(&es, &major, &minor);
    if (!es && (major > 3 || (major == 3 && minor >= 1)))
        ...

This patch changes piglit_get_gl_version() so that it returns a single
integer whose value is 10 times the GL version (e.g. 31 for GL version
3.1), and splits off the functionality for checking whether the API is
GL ES to a new function, piglit_is_gles().

Now the same logic looks like this:

    /* Are we using GL with a version of at least 3.1? */
    if (!piglit_is_gles() && piglit_get_gl_version() >= 31)
        ...

Reviewed-by: Brian Paul <brianp@vmware.com>