loop unrolling: fix couning loop analysis and full unrolling
loop unrolling: fix couning loop analysis and full unrolling

- correctly handle different relations in loop condition
- correctly handle decreasing counters
- fully unroll loops which are taken exactly one time

MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,MatzeB/libfirm,libfirm/libfirm,MatzeB/libfirm,libfirm/libfirm,libfirm/libfirm,libfirm/libfirm,MatzeB/libfirm,libfirm/libfirm