ENH support sparse matrices in LSHForest
ENH vectorise _find_longest_prefix_match
TST LSHForest benchmark script uses vectorised queries and fixed random_state
FIX not all scipy.sparse support rand with random_state
STY cleaning some LSHForest query code
COSMIT Minor changes to address review comments
DOC mention sparse matrix in LSHForest param docstrings
DOC add note on scipy.sparse.rand use
Merge pull request #3991 from jnothman/lshforest_improvements

[MRG+1] LSHForest: sparse support and vectorised _find_longest_prefix_match