configure: fix with-pjproject-bundled

The AC_ARG_WITH macro's shell variable is withval; not enableval. Purely
coincidentally, the option would work when --enable-dev-mode is given.

Also fixed a portability problem with bootstrap.sh, since -printf is not
a portable option for find.

Change-Id: I0f0e5b1a934b5af5737713834361e9c95b96b376