AppVeyor: don't build if [build appveyor] is not provided

scripts/build-appveyor.bat

@@ -5,10 +5,16 @@ SET EL=0
 ECHO =========== %~f0 ===========
 
 ECHO NUMBER_OF_PROCESSORS^: %NUMBER_OF_PROCESSORS%
-ECHO RAM [MB]:
-powershell "get-ciminstance -class 'cim_physicalmemory' | % {$_.Capacity / 1024 / 1024}"
+ECHO RAM [MB]^:
+powershell "get-ciminstance -class 'cim_physicalmemory' | %% { $_.Capacity/1024/1024}"
 IF %ERRORLEVEL% NEQ 0 GOTO ERROR
 
+::only build on AppVeyor, if explicitly stated
+ECHO APPVEYOR_REPO_COMMIT_MESSAGE^: %APPVEYOR_REPO_COMMIT_MESSAGE%
+SET BUILD_ON_APPVEYOR=0
+for /F "tokens=1 usebackq" %%i in (`powershell .\scripts\parse-commit-message.ps1 '[build appveyor]'`) DO SET BUILD_ON_APPVEYOR=%%i
+IF %BUILD_ON_APPVEYOR% EQU 0 ECHO not building, commit with [build appveyor] && GOTO DONE
+
 SET BUILD_TYPE=%configuration%
 SET BUILDPLATFORM=%platform%
 SET TOOLS_VERSION=%msvs_toolset%.0

scripts/build-local.bat

@@ -4,6 +4,8 @@ SET EL=0
 
 ECHO =========== %~f0 ===========
 
+SET APPVEYOR_REPO_COMMIT_MESSAGE=das ist ein test
+
 SET MAPNIK_GIT=3.0.5
 SET BOOST_VERSION=58
 SET FASTBUILD=1

scripts/parse-commit-message.ps1

@@ -0,0 +1,5 @@
+if($env:APPVEYOR_REPO_COMMIT_MESSAGE.ToLower().Contains($args[0].ToLower())) {
+    Write-Host '1';
+} else {
+    Write-Host '0';
+}