work on android-dev presentation

Signed-off-by: Bao Haojun <baohaojun@gmail.com>
.emacs: Do not load purcell stuff if org2pdf
bin/org2pdf: make it work for worg's presentation.org
doc/presentations/android-dev.org: Work on android-dev presentation

Signed-off-by: Bao Haojun <baohaojun@gmail.com>