Enabled the AppVeyor proxy and fixed checking of the errorlevel in the batch files.

Author: dirk

AppVeyor/Install.cmd

@@ -4,7 +4,9 @@ cd ..
 call CloneRepositories.cmd https://github.com/ImageMagick shallow
 
 if not exist "C:\Program Files (x86)\Inno Setup 5" choco install innosetup -y -version 5.5.2
+if %errorlevel% neq 0 exit /b %errorlevel%
 
 set OPTION=
 if "%1" == "x86" SET OPTION=-x86
 choco install strawberryperl -y %OPTION% -version 5.20.1.1
+if %errorlevel% neq 0 exit /b %errorlevel%

appveyor.yml

@@ -53,6 +53,7 @@ environment:
       im_name:     "source"
 
 install:
+  - ps: iex ((new-object net.webclient).DownloadString('https://raw.githubusercontent.com/appveyor/ci/master/scripts/enable-http-proxy.ps1'))
   - cd AppVeyor
   - Install.cmd %im_platform%