calchash(): work around broken RTTI.

calchash(): work around broken RTTI.

Due to the strange (although permitted by the standard) behaviour of C++
RTTI on woe32 calchash() returns different hash values for equal objects.
As a result automatic evaluation gets spectacularly broken:

examining clifford objects.....({1+t,2+x,3+y,4+z}) - ({1+t,2+x,3+y,4+z}) erroneously returned -{1+t,2+x,3+y,4+z}+{1+t,2+x,3+y,4+z} instead of 0
({1+t,2+x,3+y,4+z}) - ({1+t,2+x,3+y,4+z}) erroneously returned -{1+t,2+x,3+y,4+z}+{1+t,2+x,3+y,4+z} instead of 0
.({1+t,2+x,3+y,4+z}) - ({1+t,2+x,3+y,4+z}) erroneously returned -{1+t,2+x,3+y,4+z}+{1+t,2+x,3+y,4+z} instead of 0
({1+t,2+x,3+y,4+z}) - ({1+t,2+x,3+y,4+z}) erroneously returned {1+t,2+x,3+y,4+z}-{1+t,2+x,3+y,4+z} instead of 0
[skipped]
.......FAIL: exam_clifford.exe

This patch works around `features' of woe32 RTTI, so calchash() works
properly.