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.
Ok. Is there any way to make the option name `--with-homebrew-apr` and have it still relate to `depends_on "homebrew/apache/apr" => :optional`?