do not depend on text output of tty program
add memleak property again because #32 is not fixed
NULL fails on gcc 4.{6,8,9}
fix shadowing

/var/lib/jenkins/jobs/elektra-multiconfig-gcc-stable/workspace/build_type/Debug/gcc_version/4.6/plugins/DEFAULT/source/src/libelektra/keyset.c:1060:9:
warning: declaration of ‘index’ shadows a global declaration [-Wshadow]