Bootstrap fails because of spaces in exe path, fixed with :shell nil

The bootstrap install fails on Windows when `install-info` is under `C:\Program File\GnuWin32\bin` (the default) because of the space in the path. The problem appears to be that `el-get-build` always passes `:shell t` to `el-get-start-process` which I think is unneeded since all it does it tell `el-get-start-process` to use `start-process-shell-command` which simply prepends `shell-file-name` and `shell-command-switch` to the arg list but this is already done by `el-get-build` in the `stringp` case.

Message in `*el-get-build: el-get*`:

    'c:/Program' is not recognized as an internal or external command,
    operable program or batch file.


Excerpt from `*Backtrace*`:

    el-get-start-process-list("el-get" ((:command-name "c:/Program Files/GnuWin32/bin/install-info.exe" :buffer-name "*el-get-build: el-get*" :default-directory "c:/Users/npostavs/.emacs.d/el-get/el-get/." :shell t :sync t :program "c:/Program Files/GnuWin32/bin/install-info.exe" :args ("c:/Users/npostavs/.emacs.d/el-get/el-get/./el-get.info" "dir") ...)))
    ...
    el-get-build("el-get" (("c:/Program Files/GnuWin32/bin/install-info.exe" "c:/Users/npostavs/.emacs.d/el-get/el-get/./el-get.info" "dir")) "." t nil t)