Separates faster and slower bench alerts; sorts by delta.

tools/tests/benchalerts/Perf-Android-Nexus7-Tegra3-Arm7-Release/output-expected/stderr

 Traceback (most recent call last):
-  File "bench/check_bench_regressions.py", line 218, in <module>
+  File "bench/check_bench_regressions.py", line 259, in <module>
     main()
-  File "bench/check_bench_regressions.py", line 214, in main
-    platform_and_alg)
-  File "bench/check_bench_regressions.py", line 161, in check_expectations
-    '\n'.join(exceptions))
-Exception: Bench values out of range:
-Bench desk_baidu.skp_record_,Perf-Android-Nexus7-Tegra3-Arm7-Release-25th value 0.83 out of range [5.155, 11.033].
+  File "bench/check_bench_regressions.py", line 255, in main
+    check_expectations(bench_dict, bench_expectations, platform_and_alg)
+  File "bench/check_bench_regressions.py", line 203, in check_expectations
+    raise Exception('\n'.join(outputs))
+Exception: 
+2 Slower benche(s) (Sorted):
+Bench desk_blogger.skp_record_,Perf-Android-Nexus7-Tegra3-Arm7-Release-25th out of range [0.4, 0.6] (1.794 vs 0.5, 258.8%).
+Bench desk_amazon.skp_record_,Perf-Android-Nexus7-Tegra3-Arm7-Release-25th out of range [-1.0, 1.2] (1.213 vs 1.1, 10.2727272727%).
+
+1 Faster benche(s) (Sorted):
+Bench desk_baidu.skp_record_,Perf-Android-Nexus7-Tegra3-Arm7-Release-25th out of range [0.9, 1.0] (0.83 vs 0.939, -11.6080937167%).