WIP: avoid densifying on sparse elementwise mult
MAINT: remove NumPy < 1.6 compatibility
Merge pull request #4265 from larsmans/numpy-16

MAINT: remove NumPy <1.6 compatibility
Merge pull request #4133 from perimosocordiae/patch-4

ENH: sparse: delay densifying on sparse elementwise mult
MAINT: pchanial's improvement of input validation in sparse's __mul__
TST: improve a test by using self.spmatrix