Added the hidden `chm_factorize_p` function

This function, which calls `cholmod_factorize_p`, allows for updating
the factorization for A + beta*speye(size(A)...) without explicitly
forming the sum.  This is convenient and saves a bit of time in some
of my work.
cleanup range searchsorted methods, remove redundant hist methods
Merge pull request #2927 from dmbates/master

Add a hidden convenience function `chm_factorize_p` to LinAlg.CHOLMOD
fix #2971
Merge pull request #2970 from simonbyrne/ranges

cleanup range searchsorted methods, remove redundant hist methods
Add a DataStructures module with PriorityQueue and heap functions.
Rename DataStructures to Collections. Document.
Export Collections, not DataStructures.
"DataStructures" to "Collections" in a comment.
More specific type for index in PriorityQueue.
Rename has to haskey in PriorityQueue.
Merge pull request #2920 from JuliaLang/dcj/pq2

Add a DataStructures module with PriorityQueue and heap functions.
Merge remote-tracking branch 'upstream/master'