glxinfo: add queries and reporting for float and sRGB buffer types

glxinfo: add queries and reporting for float and sRGB buffer types

Check for the GLX_ARB_fbconfig_float and GLX_NV_float_buffer extensions
to determine if color bufs are floating point.

Check for the GLX_EXT_framebuffer_sRGB extension to determine if the
framebuffer is sRGB capable.

Increase field size for some attribs (visual ID and buffer size) to
accomodate today's larger values.

Also print missing caveats info in verbose mode.