TST: sparse: fix overlapping memory assign in test case

Doesn't work correctly on Numpy 1.5
BUG: sparse: add a version of bincount with minlength kw, for Numpy 1.5
MAINT: sparse: rename compat routines safe -> compat
ENH: sparse/sputils: add some tests for the compat routines
Merge pull request #3408 from pv/sparse-fixnumpy15-2

MAINT: sparse: Numpy 1.5 compatibility fixes