ENH: Moved kwsys_ns and kwsysEXPORT macros to Configure.h in the case of building a kwsys source file.  This allows more than one header to be included in a kwsys source file without redefining the macros.

ERR: Avoiding namespace pollution: kw_sys -> kwsys_ns.  Also undefining the macro at the correct time.

ERR: On Borland preprocessor goes into recursion which adds some weid spaces in the include name. This fixes it

ERR: Reduced requirements on preprocessor for export macro due to limitations of Mac preprocessor.  The preprocessor can be fixed by using -no-cpp-precomp, but we don't want to require that option for every source file that includes our headers.