Simplify make_seed and undo 7b44eb now that register shifts are safe

This needs to be tested more on 32-bit machines

As per discussion: https://github.com/JuliaLang/julia/commit/7b44ebe60f3e0a5e147f3124aa6ea813edadcfa0
Yield error on to_index with non-Real argument

Fixes #6017
Allow Real when scalar-ndexing on 7th+ dimension
Fix install and win-extras for Cygwin cross

- call cygpath_w on julia executable for stringpatch
- don't try to copy p7zip bin and lib into dist-extras on Cygwin
- chmod a+x on both 7z.exe and 7z.dll, before first running 7z.exe
New norm(Matrix) behavior to NEWS
Merge pull request #6037 from JuliaLang/cb/index

some indexing tweaks
fix #6050
Merge pull request #6045 from tkelman/patch-3

Fix install and win-extras for Cygwin cross
fix missing OPENLIBM_FLAGS for make install

this was breaking cross compiles
Merge pull request #6059 from tkelman/patch-2

fix missing OPENLIBM_FLAGS for make install
mention that perf.h is generated in perf.c

https://github.com/JuliaLang/julia/issues/6054

This has come up a couple of times now.
Changed selection of shift-and-invert mode in eigs. Added test for inverse iteration. Docs updated.
Change default of sigma to nothing.
Only non-empty sigma selects shift and invert mode (implies which=LM). Test updated.
Update NEWS.md
Document eye(A) when A is a dense/sparse matrix
New semantics of sigma in eigs(A, sigma)

- `sigma==nothing` specifies forward iteration (ARPACK `iparam(7)=1`), and a numeric real or complex sigma specifies inverse iteration with level shift (`iparam(7)=3` or 4 depending on `complexOP`)
add new vecnorm(x, p), generalizing and replacing normfro; also fix #6056
don't make a copy when hashing substrings
Pkg: pull requests no longer take '?expand=1'

This used to open up to the pull request but no longer does. Now it's better to just show the user the diff and let them click the "create pull request" button on that page.