Add support for --raw and --omit to js2c.

Add support for --raw and --omit to js2c.
  --raw writes the raw source data to a separate file
  --omit allows omitting the source data from the generated files.

The intention is (future) support for having the embedder optionally
store the source data 'blob' and handling it to V8::Initialize, with
the goal of reducing the binary size of V8.

The patch also contains numerous unrelated changes/refactorings in the hope of increasing maintainability. Let me know whether you agree. In particular:
- Remove some unused code.
- Do not overwrite Python built-ins (e.g. the type() function)
- Do not use a string as exception object (no longer supported in python 2.7)
- Add command line argument handling + help text.
- Split logic into:
  - PrepareSources - which reads + preprocesses the source files
  - BuildMetadata - which takes the prepared sources and generates the data the code template needs.


BUG=355539
LOG=N
R=jochen@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=20657

[vogelheim, 2014-04-04 10:55:22]

Not sure whether I'm on the right track; please have a look at this.

[jochen (gone - plz use gerrit), 2014-04-04 11:52:40]

can you reference the bug (355539) in the cl description?

lgtm

[vogelheim, 2014-04-10 14:53:38]

Committed patchset #3 manually as r20657 (presubmit successful).