Remove hard-coded Windows installation paths

- For Git, shouldn't need to look in Program Files since Windows Julia bundles Git.
- MinGW is a build-time dependency, not a user dependency. These path additions were the only reason test/spawn.jl could ever execute successfully outside of MSYS. This is a problem that can be addressed separately, and the solution should not rely on a hard-coded installation path of MSYS1.
- Python should only be needed by packages, or at build time for LLVM. Wouldn't a better solution involve PYTHONPATH or PYTHONHOME, or manage this on a package level when Python is required?
Fix error when filename is null

Seen occasionally on Windows when running test/file.jl
doc: excise nonexistent svds (Fix #6159)
Use similar instead of Array when allocating new arrays.
Export options.h referenced by julia.h
Merge pull request #6145 from tkelman/patch-3

Remove hard-coded Windows installation paths
binomial no longer uses Float64 internally.

Replaces the old accumulation step, using x=*(nn::Float64, rr::Float64)
with x::T=xt=div(widemul(x,nn), rr). Also tests for integer overflow.

Fix #6154.
document and export `widen`. closes #6169
Merge pull request #6163 from JuliaLang/cjh/fix-6154

binomial no longer uses Float64 internally.
Merge branch 'master' of https://github.com/JuliaLang/julia
also export widemul (ref #6169)

widen methods for Rational and Complex
Merge branch 'master' of github.com:JuliaLang/julia
Merge pull request #6174 from felipecruz/feature/export_options_h

Export options.h referenced by julia.h
Merge pull request #6167 from JuliaLang/anj/similar

Use `similar` instead of `Array` when allocating new arrays.
Merge pull request #6146 from tkelman/patch-4

Fix error when filename is null
fix Base.Sort.Float.issignleft bug: 0.0 before -0.0 in reverse mode.
refactoring to separate subtype and morespecific
sortperm: one way to fix #6177, but with 34% slowdown.

The approach here is to change the Perm comparison to break ties
by index values. This allows using an unstable algorithm getting
stable sortperm results but kills performance despite the switch
to quicksort.
Merge branch 'master' of github.com:JuliaLang/julia
base/ordering.jl: simplified lexicographic permutation comparison.