merged

Added tag Isabelle2016-RC5 for changeset 45adb8dc84e1

invoke perl system with explicit list -- to avoid extra /bin/sh and thus evade potential conflict of /bin/sh -> dash with bash on Debian/Ubuntu;

evade a potential conflict of /bin/bash versus /bin/sh -> dash (notably on Ubuntu and Debian) -- note that execvpe does not exist on old glibc on Ubuntu 10.04 LTS, but the environ should be unchanged;

tuned;

misc tuning;

misc tuning and updates;

misc tuning and updates;

misc tuning;

tuned whitespace;

more on "Markdown-like text structure";

more on 'consider';

tuned;

more explicit dummy proofs;

misc tuning and updates;

tuned;