gnome-autogen.sh: correct IFS value

Due to a likely copy-paste mistake, the default value of IFS was being
set to 9 spaces instead of a tab and a space.  Fix that.

https://bugzilla.gnome.org/show_bug.cgi?id=726208
gnome-common: use ACLOCAL_PATH over ACLOCAL_FLAGS

jhbuild has set this variable for more than two years.

https://bugzilla.gnome.org/show_bug.cgi?id=726208
gnome-autogen: require automake 1.11.2

This is the version of automake that introduced ACLOCAL_PATH support, so
make sure that we have it before attempting to configure the package.
gnome-autogen.sh: Fix check if stdin is a tty

Commit 7f977b021462 introduced a check if stdin is ins't a tty, and
prevent printing terminal codes in this case. But the check was wrong
and always failed.

https://bugzilla.gnome.org/show_bug.cgi?id=726892
version 3.12.0