Remove obsolete unistd.h file

The presence of this file can cause build issues when integrating glslang
into other projects.

Various build fixes when using newer GCC versions with warnings enabled

Encountered with GCC-4.7.3 in a build environment where warnings are enabled
and treated as errors.

Replace sprintf() usage with snprintf()

This fixes compilation in build environments with stricter warnings enabled

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.