Fixes format-security error when compiling ruby_193_compatible.h

When compiling the extension for Ruby 1.9 on a system that treats format-security warnings as errors (i.e. the Makefile generated for the extension contains "-Werror=format-security"), compilation would fail with the following error:

```
compiling atomic_boolean.c
In file included from atomic_boolean.c:5:0:
ruby_193_compatible.h: In function 'rb_error_arity':
ruby_193_compatible.h:20:3: warning: passing argument 2 of 'rb_raise' makes pointer from integer without a cast [enabled by
 default]
   rb_raise(rb_eTypeError, err_mess);
   ^
In file included from /usr/include/ruby-1.9.1/ruby.h:32:0,
                 from atomic_boolean.c:1:
/usr/include/ruby-1.9.1/ruby/ruby.h:1172:27: note: expected 'const char *' but argument is of type 'VALUE'
 PRINTF_ARGS(NORETURN(void rb_raise(VALUE, const char*, ...)), 2, 3);
                           ^
/usr/include/ruby-1.9.1/ruby/ruby.h:42:3: note: in definition of macro 'PRINTF_ARGS'
   decl __attribute__((format(printf, string_index, first_to_check)))
   ^
/usr/include/ruby-1.9.1/ruby/ruby.h:1172:13: note: in expansion of macro 'NORETURN'
 PRINTF_ARGS(NORETURN(void rb_raise(VALUE, const char*, ...)), 2, 3);
             ^
In file included from atomic_boolean.c:5:0:
ruby_193_compatible.h:20:3: error: format not a string literal and no format arguments [-Werror=format-security]
   rb_raise(rb_eTypeError, err_mess);
   ^
cc1: some warnings being treated as errors
make: *** [atomic_boolean.o] Error 1
```

This updates these functions to work more like the original copies (found in the Ruby 2.0+ source code), which avoids this compilation error.

Author: Rob Percival

ext/concurrent/ruby_193_compatible.h

@@ -5,7 +5,7 @@
 
 #define UNLIMITED_ARGUMENTS (-1)
 
-static inline void rb_error_arity(int argc, int min, int max)
+static inline VALUE rb_error_arity(int argc, int min, int max)
 {
   VALUE err_mess = 0;
   if (min == max) {
@@ -17,12 +17,12 @@ static inline void rb_error_arity(int argc, int min, int max)
   else {
     err_mess = rb_sprintf("wrong number of arguments (%d for %d..%d)", argc, min, max);
   }
-  rb_raise(rb_eTypeError, err_mess);
+  return rb_exc_new3(rb_eTypeError, err_mess);
 }
 
 #define rb_check_arity(argc, min, max) do { \
   if (((argc) < (min)) || ((argc) > (max) && (max) != UNLIMITED_ARGUMENTS)) \
-  rb_error_arity(argc, min, max); \
+  rb_exc_raise(rb_error_arity(argc, min, max)); \
 } while(0)
 
 #endif