orion.h:  Quell compiler warning on MinGW

Quell the following error on MinGW:

  CC       orion.lo
In file included from ../../hamlib-3.0~git/tentec/orion.c:86:0:
../../hamlib-3.0~git/tentec/orion.h:34:0: warning: "TRUE" redefined [enabled by default]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/windef.h:55:0: note: this is the location of the previous definition
../../hamlib-3.0~git/tentec/orion.h:35:0: warning: "FALSE" redefined [enabled by default]
c:\mingw\bin\../lib/gcc/mingw32/4.6.2/../../../../include/windef.h:52:0: note: this is the location of the previous definition

which seemed to be caused by the values to TRUE and FALSE being enclosed
in parentheses.