autogen.sh heads up

[Tim Janik <timj gtk org>]

hi all.

i've just applied the following changes to the autogen.sh of glib,
pango and gtk+:
- exit with $? instead of 1 in case of failure
- exit with $? if ./configure failed
  (that's so autogen.sh && make lines work)
- removed --enable-gtk-doc option
- added $AUTOGEN_CONFIGURE_ARGS

so people who want to automatically get docs build from their
CVS tree will want to export AUTOGEN_CONFIGURE_ARGS=--enable-gtk-doc
from now on.

---
ciaoTJ