embed.pl now reads *var*.h to do its stuff.

embed.pl now reads *var*.h to do its stuff.
Split generated embed.h into two - new embedvar.h
is #included when 'op' etc. will not mess up proto.h etc.
Removed #define foo (thr->Tfoo) from thread.h
Added some 'missing' symbols to global.sym, removed
those in the *var*.h files
Has build all MULTIPLICITY/USE_THREADS options on win32
with VC++ (and passed tests), but not with exactly this set
of files.

p4raw-id: //depot/ansiperl@338