BLD: Replaced batch script for building dependency packages

with powershell.  Easier to write.

Check $LastExitCode when running non-powershell

appveyor.yml

@@ -106,19 +106,17 @@ install:
   # https://blog.ionelmc.ro/2014/12/21/compiling-python-extensions-on-windows/ for 64bit C compilation
   - ps: copy .\ci\appveyor\vcvars64.bat "C:\Program Files (x86)\Microsoft Visual Studio 10.0\VC\bin\amd64"
 
-  - cmd: |
-      FOR /D %%r IN (conda/*) DO (
-        IF NOT "%%r" == "zipline" (
-          %CMD_IN_ENV% conda build "conda/%%r" --python=%CONDA_PY% --numpy=%CONDA_NPY% --skip-existing -c quantopian
-
-          FOR /f "tokens=* USEBACKQ" %%F IN (`%CMD_IN_ENV% conda build "conda/%%r" --python=%CONDA_PY% --numpy=%CONDA_NPY% --output`) DO (
-            SET RECIPE_OUTPUT=%%F
-          )
-          IF EXIST "%RECIPE_OUTPUT%" (
-            %CMD_IN_ENV% anaconda -t %ANACONDA_TOKEN% upload "%RECIPE_OUTPUT%" -u quantopian --label ci
-          )
-        )
-      )
+  - ps: >-
+      foreach ($recipe in dir .\conda -dir -name) { `
+        if ($recipe -eq "zipline") { continue } `
+        iex "$env:CMD_IN_ENV conda build conda/$recipe -q --python=$env:CONDA_PY --numpy=$env:CONDA_NPY --skip-existing -c quantopian"; `
+        if ($LastExitCode -ne 0) { throw "Command failed with exit code $LastExitCode." } `
+        $RECIPE_OUTPUT=conda build conda/$recipe --python=$env:CONDA_PY --numpy=$env:CONDA_NPY --output; `
+        if (Test-Path $RECIPE_OUTPUT) { `
+          anaconda -t $env:ANACONDA_TOKEN upload "$RECIPE_OUTPUT" -u quantopian --label ci; `
+          if ($LastExitCode -ne 0) { throw "Command failed with exit code $LastExitCode." } `
+        } `
+      }
   - cmd: '%CMD_IN_ENV% conda build conda/zipline --python=%CONDA_PY% --numpy=%CONDA_NPY% -c quantopian'
 
   - cmd: conda create -n testenv --yes --use-local pip python=%PYTHON_VERSION% numpy=%NUMPY_VERSION% scipy=%SCIPY_VERSION% ta-lib=0.4.9 bcolz=0.12.1 numexpr=2.4.6