Fix disappearing exceptions in GenerateProtoBuf.kt

Any exception caught during the generation (e.g. about an incompatible version)
is lost because of 'System.exit(0)' in 'finally'

generators/src/org/jetbrains/jet/generators/protobuf/GenerateProtoBuf.kt

@@ -17,8 +17,6 @@
 package org.jetbrains.jet.generators.protobuf
 
 import com.intellij.execution.util.ExecUtil
-import com.intellij.execution.process.BaseOSProcessHandler
-import java.util.concurrent.ExecutorService
 import java.io.File
 
 // This file generates protobuf classes from formal description.
@@ -45,6 +43,10 @@ fun main(args: Array<String>) {
         modifyAndExecProtoc(commonProto, "compiler/tests")
         modifyAndExecProtoc(javaProto, "compiler/tests")
     }
+    catch (e: Throwable) {
+        e.printStackTrace()
+        throw e
+    }
     finally {
         // Workaround for JVM hanging: IDEA's process handler creates thread pool
         System.exit(0)