Changes

Bug 1219: IOUtil.testDirExe: Disable 'existingExe' DEBUG_EXE feature by
hardcoded 'DEBUG_EXE_EXISTING_FILE = false'
This is required for security, i.e. not allowing to execute any
pre-existing files!
In case we need to manually debug this issue, we can re-enable it
manually and locally, but not in public builds!