The gl_in array has a special path due to context-specific
gl_MaxPatchVertices, making the code out of order for tagging built-ins.
This commit moves the tagging to the correct location.
This also fixes issue #80.

Expand to full isConstant() implementation.
Fix disassembler to generate texture look-up masks.

Generate correct image operand mask for Offset and ConstOffset(#77) and correct arg # for rect. texelFetchOffset.

This fixes a bug where a token that could be a keyword in one version
is not a keyword in another version, but treated like a non-member after
a "." dereference.

4 components are needed when used a texture, but not an image, which multiplies
layers and faces into the same coordinate.  This fixes it from using 4 everywhere,
to only using 4 for textures and 3 for images.

SPV non-determinism: Fixed subtle issue that causes tests to fail in VS2013 in some configs.

Depending on specific optimization settings VS2013 will sometimes
execute the operands to

new Instruction(builder.getUniqueId(), builder.makeBoolType(), OpPhi)

left-to-right, and sometimes right-to-left. Since makeBoolType can
also call getUniqueId(), the IDs to the OpPhi can sometimes be swapped.

This guarantees an explicit ordering of the Ids so that tests work
reliably.

SPIRV: Add image instruction support and atomic counter support.

the expectations of old GLSL shadow*() lookups.

Structured control-flow rules allow leaving the middle of a construct through
a return, but not through a jump to a block that does a return.

Addresses issue #58.

This generally simplifies access chain generation, with far fewer  type conversions.
It is particularly important to future SPIR-V changes where there is less aggregate
type uniqueness due to carrying different layout information with the type.

This includes run-time block.member.length() (OpArrayLength).

Front-end Arrays of arrays: Add ES-specific checks and tests.  AoA should be quite close to done now.

Sync local master branch from the upstream