Changes

Changes from Mercurial (hg http://isabelle.in.tum.de/repos/isabelle/ default)

Summary

1. merged
2. avoid "exec" to change the winpid;
3. clarified check of root process on Windows (NB: the winpid is less stable than the Cygwin/Posix pid, so it needs to be "patched" into the the bash script, instead of bash_process.c);
4. fast approximation of test for process group (NB: initial process might already be terminated, while background processes are still running);
5. clarified signature;
6. rebuild executable for x86_64-darwin;
7. clarified command-line;
8. update Linux base-line;
9. tuned comments;
10. tuned signature;
11. simplified typesetting of \<guillemotleft>...\<guillemotright>;