Fixed VS2015 build

SPIR-V: Return undefined values from implicit returns instead of dummy

Add missing OpTypeSampledImage to prevent unknown type error from SPV…

Previously if a non-void function implictly returned, a dummy variable
was created as return value. Now instead it returns the result of the
OpUndef instruction. This better conveys the presence of undefined
behavior to SPIR-V consuming tools (and humans).

It also saves one ID per occurrence...

There will be subsequent commits to refine semantics, esp. version-specific semantics,
as well as I/O functionality and restrictions.

Note: I'm getting white-space differences in the preprocessor test results,
which I'm not checking in.  I think they need to be tagged as binary or something.

Added some const as well. This will remove camouflage of the next commit,
which will add the bulk of Array of Array semantics and functionality.
(Note the basic grammar and data structure is already in place.)

Add getStringNameOrNum() in TSourceLoc.

Compile fixes for gcc -Wall

Remove unsigned/size_t downcast (warning when building on x64)

Remove unused members from TPpContext

The ErrMsg and ifloc members were unused or had no effect.

#include directive support

Now extensions required by preprocessor should be checked via
the ppRequireExtensions method. This is more clear and coherent
with the rest of the code.

Revisioning: Include GLSL.std.450 version.  Also, the revision.h script now includes redirection to revision.h.

The new make-revision script regenerates glslang/Include/revision.h,
used as it always has been, but made with a git-tag version and the
the number of commits on master.

I have a pre-commit hook that will automatically do this on master,
likely often enough to work in practice, without needing pull requests
to include it.

Also changed the includer interface to let it return the actual
full path of the included file.

After parsing a #include directive, we push a TokenizableString
which contains the content of the included file into the input
stack. Henceforth, tokens will be read from the newly pushed
TokenizableString. However, the scanner in TParseContext still
points to the previous input stream. We need to update the scanner
to point to the new input stream inside TokenizableString. Thus,
the setCurrent{String|Line|..} method in TParseContext updates
the status of the correct input stream. After finishing the newly
pushed TokenizableString, we need to restore the scanner to the
previous input stream.

This patch introduces a new extension, GL_GOOGLE_include_directive,
to enable support #include directives. It depends on the extension
GL_GOOGLE_cpp_style_line_directive.

When an include directive is recognized by the preprocessor, it
executes a callback on the filepath argument to obtain the file
contents.  That way the compilation client can deal with the file
system, include paths, etc.

Currently only accepts quoted filepaths -- no angle brackets yet.

Add mechanism for specifying names for source strings.

Expose a new method setStringsWithLengthsAndNames() in the interface
which allows the caller to set descriptive names for source strings.
These names can be used in error messages.

Extend the syntax of #line and __FILE__ to support filename strings.

The implementation is done via introducing a new extension 
GL_GOOGLE_cpp_style_line_directive using the extension framework.

The purpose is to support cpp-style #line directives, which is
required by #include.

Use requireExtensions() to check GL_GOOGLE_cpp_style_line_directive
is turned on. Add register more tests for running.