RFR: 174: git-webrev should support taking file list via STDIN

[Erik Helin]

Hi all,

please review this small patch that adds support for `git-webrev` to take the list of files that should be included via STDIN.

Thanks,
Erik

## Testing
- [x] Manual testing of `git-webrev` and passing files to include via STDIN

----------------

Commits:
 - 218600ee: 174: git-webrev should support taking file list via STDIN

Changes: https://git.openjdk.java.net/skara/pull/276/files
 Webrev: https://webrevs.openjdk.java.net/skara/276/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-174
  Stats: 8 lines in 2 files changed: 6 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/skara/pull/276.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/276/head:pull/276

PR: https://git.openjdk.java.net/skara/pull/276