Fix formatting error in eigs doc
Fix code block formatting error in control flow doc
Fix Makefile typo
Add orphan tags to non-default docbuild targets

The orphan tag suppresses Sphinx's complaints about their exclusion from certain docbuild targets
restore helpful message for sqrt(-1)
Merge branch 'master' of https://github.com/JuliaLang/julia
fix one more issue in commit 9b5b197695ebe05bb95cf60a0b028e3677529c8f
base/operators.jl: remove harmful (incorrect) fallback for cmp.

This was causing cmp(Uint128,Uint128) to give wrong answers. The
other more general fallback that already exists is better.