Support ISG1 and OSG1

These are input an output signatures with Stream and MinPrecision.
i.e. D3D11_SIGNATURE_PARAMETER_DESC  instead of
D3D10_SIGNATURE_PARAMETER_DESC
Merge from master
Support boolean-typed constants using integers.

Boolean constants are now recognised. They are declared as integer in
the GLSL code - this allows implicit conversions to integer and bool
still consumes 4-bytes in GLSL.