mtest vs. test: add possibility to exit testing

'mtest' can now optionally only run a given amount of loops.
the first parameter <n> when invoking 'mtest' is considered to determine
the amount
when <n> is in the range -63..-1: mtest will run 2^-n runs
when <n> is > 0: mtest will run n runs
else: mtest will exit immediately
Revert "balancing multiplication like that in Ruby 1.9"

This reverts commit e68439aae10d003250afa6c1f57025bfee5f82ed.

Conflicts:
	bn_mp_balance_mul.c
	makefile
update after removing balance multiplication
initial revision
update README
add new make target 'test_standalone'