Call tchdboptimize only in 1% of the OpenTokyoDatabase() calls

Even though we call non-reentrant rand() from multiple thread contexts,
there is no harm done even if bad random numbers are returned.
(cherry picked from commit 3d95e9226cd0a38d077333d0cdec4ae85d6a0d0d)

Conflicts:
	libpromises/dbm_tokyocab.c