[GSOC] Update 4: Unification of tag -l, branch -l and for-each-ref

Hello All,

As part of GSoC I'm working on the Unification of 'for-each-ref', 'tag -l' and 'branch -l'. Sorry for the lack of update since Jun 14, was a little busy with an exam I had. Now thats over, I will be working more on the project.

Current Progress:

1. Building ref-filter.{c,h} from for-each-ref.
This is the process of creating an initial library for the unification
by moving most of the code from for-each-ref to ref-filter.{c,h}.
Merged into next

2. Add options to ref-filter.
This includes the porting of --points-at, --contains, --merged,
--no-merged options from builtin/branch.c and builtin/tag.c, Also the
implementation of these options into for-each-ref.
The last version (v8) is posted here:
http://thread.gmane.org/gmane.comp.version-control.git/273569
Currently waiting for comments.

3. Port builtin/tag.c to use ref-filter.
Here we port tag.c to use ref-filter and also port the --format,
--sort and --merged and --no-merged options to builtin/tag.c.
The "RFC" version is posted and I'm waiting for comments from the list:
thread.gmane.org/gmane.comp.version-control.git/272654
Will post v2 soon.

Next Plans: I'm currently working on porting over builtin/branch.c to use ref-filter.{c,h}, will be pushing intermediate code to my Github repository. Currently looking at what all branch.c needs in ref-filter and adding respective options to ref-filter. https://github.com/KarthikNayak/git

Thanks to everyone who has helped :)