ENH much more efficient sparse min/max with axis
TST/FIX better test coverage for minmax, and handle 0-size
TST ndarray-compatible handling of zero-size arrays in max/min
ENH still faster min/max using ufunc.reduceat

H/T @jaimefrio
DOC add comments to min/max
FIX for Numpy 1.5 cannot use where
ENH factor out minor-axis reduce operation and reuse for sum
FIX Minor fixes and cosmetic changes to min/max
FIX min/max for BSR
TST test edge cases for min/max
BUG: sparse: Numpy < 1.8 compatibility
TST: sparse: extend sum & minmax test diversity
BUG: sparse: fix dtype of bsr_matrix.transpose of an empty matrix
Merge branch 'pr-3248' into pr-3248-merge

Conflicts:
	scipy/sparse/data.py
	scipy/sparse/tests/test_base.py