Fixed outputof to redirect all standard streams.

Workaround until https://github.com/premake/premake-core/pull/428 is closed.

build/scripts/Provision.lua

@@ -83,7 +83,7 @@ end
 
 function brew_install(pkg)
 	-- check if package is already installed
-	local res = os.outputof("brew ls --versions " .. pkg)
+	local res = outputof("brew ls --versions " .. pkg)
 	if string.is_empty(res) then
 		execute("brew install " .. pkg)
 	end 

build/scripts/Utils.lua

@@ -9,6 +9,13 @@ function cat(file)
   return output
 end
 
+function outputof(cmd, quiet)
+    local file = assert(io.popen(cmd .. " 2>&1", "r"))
+    local output = file:read('*all')
+    file:close()
+    return output
+end
+
 function execute(cmd, quiet)
   print(cmd)
   if not quiet then
@@ -69,7 +76,7 @@ end
 
 function git.rev_parse(dir, rev)
   local cmd = "git -C " .. path.translate(dir, sep) .. " rev-parse " .. rev
-  return os.outputof(cmd)
+  return outputof(cmd)
 end
 
 function http.progress (total, curr)