Generates fragment and vertex shader execution tests for the built-in
functions floatBitsToInt(), floatBitsToUint(), intBitsToFloat(), and
uintBitsToFloat().

Functions are tested under
	GLSL 1.30 + ARB_shader_bit_encoding (uses uint, must be 1.30)
	GLSL 1.50 + ARB_gpu_shader5 (requires 1.50)
	GLSL 4.00

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> [v1]

v2: Do not test subnormal values, since some hardware flushes them to
    zero. Fix value of smallest normalized value.