removing compiler warnings (Visual C++ /W4)
* Jamfile, src/otvalid/{otvcommn.h,otvgdef.c,otvgpos.c,otvgsub.c,
otvjstf.c}: modified the code to use a different pre-processor trick
to implement the OTV_NEST1, OTV_NEST2 and OTV_NEST3 macros. The code
now compiles neatly with Visual C++. The 'otvalid' module has been
put in the Jamfile build again.