Front-end: Fix known crashes by early exit on error (issue #29, issue #34, issue #35).

Added -C option to request cascading errors.  By default, will exit early,
to avoid all error-recovery-based crashes.

This works by simulating end-of-file in input on first error, so no
need for exception handling, or stack unwinding, or any complex error
checking/handling to get out of the stack.

glslang/MachineIndependent/ShaderLang.cpp

@@ -809,8 +809,8 @@ struct DoPreprocessing {
     explicit DoPreprocessing(std::string* string): outputString(string) {}
     bool operator()(TParseContextBase& parseContext, TPpContext& ppContext,
                     TInputScanner& input, bool versionWillBeError,
-                    TSymbolTable& , TIntermediate& ,
-                    EShOptimizationLevel , EShMessages )
+                    TSymbolTable&, TIntermediate&,
+                    EShOptimizationLevel, EShMessages)
     {
         // This is a list of tokens that do not require a space before or after.
         static const std::string unNeededSpaceTokens = ";()[]";