Avoid duplicates in sprand
sprand: handle all-zero matrix without error
doc: a couple more edits to the FAQ entry on integer arithmetic.
doc: FAQ copy fixes.
Merge pull request #4726 from JuliaLang/teh/sprand

WIP: Avoid duplicates in sprand
fix #4917, better checking of module syntax objects
fix #4919, macroexpander bug in "using" etc.
Make sqrtm work for vectors
Merge branch 'master' into arrOrderPerf
DOC: Code/timings now appear in same order

Also removed "Remember" from section title

Also added link in arrays section