native-fetcher: fix to work with nginx 1.5.8+

nginx 1.5.8 changed the resolver api, which the native fetcher uses.

Fixes #578.

Squash-merge of @dinic's #581.
readme: release 1.7.30.2
fix bug in NgxFetch#content_length_
release: prepare 1.7.30.3
Merge pull request #600 from pagespeed/huibao-prepare-release-1.7.30.3-beta

release: prepare 1.7.30.3
Merge pull request #602 from tcpper/fix_ngx_fetch_content_length

fix bug in NgxFetch#content_length_
Don't call chown() when initializing config dirs unless owner != worker user.
Merge pull request #621 from jart/dont-chown

Security Fix: Don't call chown() unless necessary.
Update README.md

nginx version update
Merge pull request #623 from pnommensen/patch-1

Update README.md
version update 

1.4.5 to 1.4.6 http://nginx.org/en/CHANGES-1.4
Merge pull request #632 from pnommensen/patch-2

1.4.5 to 1.4.6 update
Update README.md

Don't know how I missed that.
Merge pull request #633 from pnommensen/patch-2

readme: use nginx 1.4.6
release: build against backported change
Merge pull request #635 from pagespeed/huibao-prepare-1.7.30.4-release

release: build against backported change
release: udpate version number 1.7.30.3 to 1.7.30.4
Merge pull request #636 from pagespeed/huibao-prepare-1.7.30.4-release

release: update version number 1.7.30.3 to 1.7.30.4
Change version 1.7.30.3 to 1.7.30.4
merge commit: merge 1.7.30.4 into master