tomcat-native: add --with-homebrew-apr option

Yosemite ships with APR 1.4.8. This new option
allows using newer versions (eg. 1.5.1) from the
homebrew/apache tap.
Or alternatively `--with-brewed-apr` which would make it consistent with options I see in the [git formula](https://github.com/Homebrew/homebrew/blob/master/Library/Formula/git.rb) e.g. `--with-brewed-openssl`, `--with-brewed-curl`, `--with-brewed-svn`.