dri2proto: Add DRI2GetParam request

dri2proto: Add DRI2GetParam request

Bump protocol version to 1.4.
Bump package version to 2.7.

This new protocol request effectively allows clients to perform feature
detection on the DDX.

If I had DRI2GetParam in June 2011, when I was implementing support in the
Intel DDX and Mesa for new hardware that required a new DRI2 attachment
format, then I could have avoided a week of pain caused by the necessity
to write a horrid feature detection hack [1] in Mesa. In the future, when
the work begins to add MSAA support to the Intel DDX, having a clean way
to do feature detection will allow us to avoid revisiting and expanding
that hack.

[1] mesa, commit aea2236a, function intel_verify_dri2_has_hi

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Ian Romanick <idr@freedesktop.org>
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>