Sort out predefined SWIG-specific macros

Ensure that SWIG_VERSION is defined both at SWIG-time and in the
generated C/C++ wrapper code (it was only defined in the wrapper
for some target languages previously).

SWIGGO and SWIGJAVASCRIPT are now defined in the generated wrappers
to match behaviour for all other target languages.

Stop defining SWIGVERSION in the wrapper.  This only happened as a
side-effect of how SWIG_VERSION was defined but was never documented and
is redundant.

The new testcase also checks that SWIG is defined at SWIG-time but not
in the generated wrapper, and that exactly one of a list of
target-language specific macros is defined.

Fixes #1050

Lib/java/java.swg

@@ -4,6 +4,8 @@
  * Java typemaps
  * ----------------------------------------------------------------------------- */
 
+%include <typemaps/swigversion.swg>
+
 %include <javahead.swg>
 
 /* The jni, jtype and jstype typemaps work together and so there should be one of each.