vup: make 'v up' work from release archive, without a .git folder

cmd/tools/vup.v

@@ -11,21 +11,18 @@ fn main() {
 
 	println('Updating V...')
 
-	// git pull
-	git_result := os.exec('git pull --rebase origin master') or {
-		panic(err)
-	}
-
-	if git_result.exit_code != 0 {
-		if git_result.output.contains('Permission denied') {
-			eprintln('have no access `$vroot`: Permission denied')
+	if !os.exists('.git') {
+		// initialize as if it had been cloned
+		git_command('init')
+		git_command('remote add origin https://github.com/vlang/v')
+		git_command('fetch')
+		git_command('reset --hard origin/master')
+		git_command('clean --quiet -xdf --exclude v.exe --exclude cmd/tools/vup.exe')
 	} else {
-			eprintln(git_result.output)
-		}
-		exit(1)
+		// pull latest
+		git_command('pull origin master')
 	}
 
-	println(git_result.output)
 	v_hash := util.githash(false)
 	current_hash := util.githash(true)
 	// println(v_hash)
@@ -77,3 +74,21 @@ fn backup(file string) {
 	}
 	os.mv(file, backup_file)
 }
+
+fn git_command(command string) {
+	vexe := pref.vexe_path()
+	vroot := os.dir(vexe)
+
+	git_result := os.exec('git $command') or {
+		panic(err)
+	}
+
+	if git_result.exit_code != 0 {
+		if git_result.output.contains('Permission denied') {
+			eprintln('have no access `$vroot`: Permission denied')
+		} else {
+			eprintln(git_result.output)
+		}
+		exit(1)
+	}
+}