Add automatic VERSION file generation

.gitignore

@@ -3,3 +3,4 @@
 build
 out
 exe-wrapper/sheepit-wrapper.exe
+src/main/resources/VERSION

build.gradle

@@ -13,9 +13,24 @@ compileJava {
 	options.compilerArgs << '-XDignore.symbol.file'
 }
 
+task generateVersionFile {
+	def stdout = new ByteArrayOutputStream()
+	def result = exec {
+		ignoreExitValue true
+		commandLine "git", "describe", "--tags", "--always"
+		standardOutput = stdout
+	}
+	if(result.getExitValue() == 0) {
+		new File(projectDir, "src/main/resources/VERSION").text = stdout.toString() - "v"
+	} else {
+		logger.warn("Warning: automatic version detection failed")
+	}
+}
+
 shadowJar {
 	exclude 'OSGI-OPT/'  // args4j garbage
 }
+tasks.shadowJar.dependsOn(generateVersionFile)
 
 repositories {
 	mavenCentral()