Adjustments for julia-v1.7.0

[dmbates]

When the workaround for JuliaLang/julia#40048 is merged we can start testing on julia-v1.7.0-DEV

In test/runtests.jl we should replace the call to determine the BLAS in use with BLAS.get_config() for v1.7.0-DEV

A couple of instances of qr(x, Val(true)) need to be replaced by qr(x, ColumnNorm()) for recent versions of v1.7.0-DEV.

[palday]

I had already started tinkering with this locally. 😄 I'll take care of it.

If 1.6 really does become the next LTS, then we should support it until we absolutely need some killer feature from a point release, but I think we can start wrapping some of the incremental improvement and the like in@static to make it really obvious what we can cut when we drop support for 1.6.

On a related note: should we drop all pre 1.6 support with the 4.0 release?

[dmbates]

Thanks for volunteering.

I feel that we should drop all pre 1.6 support if and when it becomes the LTS release.

[palday]

(Please let that come to pass and soon .... or maybe 1.7 as an LTS, so that we get the BLAS improvements....)