Workaround for openSUSE and Fedora

- Added automatic download for Ivy itself (c.f. http://ant.apache.org/ivy/history/2.2.0/install.html), so we don't need to install Ivy manually anymore.
- Added linux/help/jhindexer.h because some distos have /usr/bin/jh2indexer instead of /usr/bin/jhindexer

I think these commits fix the build failure on openSUSE and Fedora.