Support building Git with Visual Studio

The bits about .git/branches/* have been dropped from the series.
We may want to drop the support for it, but until that happens, the
tests should rely on the existence of the support to pass.

* js/visual-studio: (23 commits)
  git: avoid calling aliased builtins via their dashed form
  bin-wrappers: append `.exe` to target paths if necessary
  .gitignore: ignore Visual Studio's temporary/generated files
  .gitignore: touch up the entries regarding Visual Studio
  vcxproj: also link-or-copy builtins
  msvc: add a Makefile target to pre-generate the Visual Studio solution
  contrib/buildsystems: add a backend for modern Visual Studio versions
  contrib/buildsystems: handle options starting with a slash
  contrib/buildsystems: also handle -lexpat
  contrib/buildsystems: handle libiconv, too
  contrib/buildsystems: handle the curl library option
  contrib/buildsystems: error out on unknown option
  contrib/buildsystems: optionally capture the dry-run in a file
  contrib/buildsystems: redirect errors of the dry run into a log file
  contrib/buildsystems: ignore gettext stuff
  contrib/buildsystems: handle quoted spaces in filenames
  contrib/buildsystems: fix misleading error message
  contrib/buildsystems: ignore irrelevant files in Generators/
  contrib/buildsystems: ignore invalidcontinue.obj
  Vcproj.pm: urlencode '<' and '>' when generating VC projects
  ...