os.read_file(): replace C code with V, return ?string, handle errors

everywhere

compiler/main.v

@@ -762,13 +762,19 @@ fn new_v(args[]string) *V {
 	// Location of all vlib files
 	mut lang_dir = ''
 	// First try fetching it from VROOT if it's defined
+	for { // TODO tmp hack for optionals
 	vroot_path := TmpPath + '/VROOT'
 	if os.file_exists(vroot_path) {
-		vroot := os.read_file(vroot_path).trim_space()
+		mut vroot := os.read_file(vroot_path) or {
+			break
+		}
+		vroot=vroot.trim_space() 
 		if os.dir_exists(vroot) && os.dir_exists(vroot + '/builtin') {
 			lang_dir = vroot
 		}
 	}
+	break
+	}
 	// no "~/.vlang/VROOT" file, so the user must be running V for the first 
 	// time.
 	if lang_dir == ''  {

compiler/scanner.v

@@ -32,9 +32,13 @@ fn new_scanner(file_path string) *Scanner {
 	if !os.file_exists(file_path) {
 		panic('"$file_path" doesn\'t exist')
 	}
+	text := os.read_file(file_path) or {
+		panic('scanner: failed to open "$file_path"')
+		return &Scanner{}
+	}
 	scanner := &Scanner {
 		file_path: file_path
-		text: os.read_file(file_path)
+		text: text
 		fmt_out: new_string_builder(1000)
 	}
 	// println('new scanner "$file_path" txt.len=$scanner.text.len')