when calling shell-file-name, don't need :shell t
a fix that doesn't break existing recipes

el-get-build should use :shell t to support "./configure" commands,
but el-get-start-process-list should shell-quote-argument the :program
argument to avoid problems with executables in funny paths.
Merge pull request #1191 from npostavs/4.stable

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