Avoid allocations in givens

One problem here was that convert on tuples calls convert_tuple even if
no conversion is necessary, and convert_tuple is a built-in that needs
a jl_tuple_t. A second problem was that the tuple elimination pass runs
after the inlining pass, so the constructor wasn't getting inlined.
Fix floatx and complexx for AbstractArrays.
Document VERSION checking. (Ref. #6147)
Merge pull request #6233 from JuliaLang/sjk/alloc-givens

Avoid allocations in givens
pkg: JULIA_EXE -> julia-basic in test!
Merge pull request #19 from JuliaLang/master

merge 4f3017e from upstream