This means that gflags no longer leaks config.h, so I had to fix a bug
in glog.bzl where config.h is generated at the wrong path.
I also switched to the best-practice for depending on git repositories,
ie using http_archive with a mirror.
This commit addresses a few issues:
1. No longer leak config.h in a way similar to
https://github.com/gflags/gflags/issues/233
The solution of prefixing the path by 'glog_internal' is modified from
https://github.com/gflags/gflags/issues/234
2. No longer expose internal headers.
3. Replace PACKAGE_NAME with native.package_name()
4. Uers can choose namespaces via the newly added 'namespace' keyword.
5. Replace glob with explicitly listing of files.
6. Make the genrules more compact using pythonic list construction.
