make dev script more robust, fix #556

dev

@@ -1,7 +1,8 @@
-#!/bin/sh
+#!/bin/bash
+set -e
 VENV=../venv.mitmproxy
 
-virtualenv $VENV
+python2 -m virtualenv $VENV
 source $VENV/bin/activate
 pip install --src .. -r requirements.txt
 

dev.bat

@@ -2,8 +2,11 @@
 set VENV=..\venv.mitmproxy
 
 virtualenv %VENV%
+if %errorlevel% neq 0 exit /b %errorlevel%
 call %VENV%\Scripts\activate.bat
+if %errorlevel% neq 0 exit /b %errorlevel%
 pip install --src .. -r requirements.txt
+if %errorlevel% neq 0 exit /b %errorlevel%
 
 echo.
 echo * Created virtualenv environment in %VENV%.