TST: test_numdiff, lower precision, fails sometimes, see #971
REF: numdiff add lower bound on epsilon, closes #072
REF/TST numdiff: use abs for epsilon, use allclose in some tests
TST lower precision, failure py>2.6 numpy>1.6.1
TST: AR predict tests: switch to allclose see #910
Merge pull request #975 from josef-pkt/misc_fixes_10

Misc fixes 10 numdiff closes #972