Fixed errorlevel/$lastexitcode handling based on $psake.build_success…

…, so that it works consistently for psake.ps1 and psake.cmd in both PowerShell window or Command Prompt window.

psake.cmd

@@ -4,7 +4,10 @@ if '%1'=='/?' goto help
 if '%1'=='-help' goto help
 if '%1'=='-h' goto help
 
-powershell -NoProfile -ExecutionPolicy Bypass -Command "& '%~dp0\psake.ps1' %*; if ($psake.build_success -eq $false) { exit 1 } else { exit 0 }"
+powershell -NoProfile -ExecutionPolicy Bypass -Command "& '%~dp0\psake.ps1' %*"
+if errorlevel 1 (
+    exit /b 1
+)
 goto :eof
 
 :help

psake.ps1

@@ -44,3 +44,6 @@ if (-not(test-path $buildFile)) {
 } 
 
 invoke-psake $buildFile $taskList $framework $docs $parameters $properties $initialization $nologo
+if (-not($psake.build_success)) {
+    exit 1
+}