Make version_git.sh work on older versions of git.

The --count option to git-rev-list was introduced in git version 1.7.x
for 1 < x < 12. When base/version_git.sh is run on versions of git
without this option, a long help message is generated (cluttering up
make output) and generating an incorrect base/version_git.jl.
version_git.sh: cope with wcs that emit whitespace.

Some versions of wc (notably the one supplied by OS X) prepend
whitespace to the output of `wc -l`, breaking the indentation of the
generated version_git.jl. We strip this using only tr(1) features
specified in
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/tr.html.
Replace calls to tr with calls to sed

We're already using sed elsewhere in the script.
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)
patch up error behavior of sqrt after 244ec92f55bb5433898c5a859a0cb452aafa1673
export jl_null and jl_subtype. fixes #6156
fix #6161
Use similar instead of Array when allocating new arrays.
Correct singular/plural mismatch
Merge pull request #6166 from catawbasam/patch-1

Correct singular/plural mismatch
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.
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