Add support for the "--" command line operator to allow working on filenames starting with the "-" character

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Attempt to use cwebp to compress a file that has a filename starting with 
the "-" character.

What is the expected output? What do you see instead?
The expected outcome (according to POSIX) is to treat all arguments after the 
"--" operator as positional arguments, even if they look like options or named 
arguments. 
Something like "cwebp -m 6 -o file.webp -- -abc123.jpg" should work, instead 
cwebp outputs "Error! Unknown option '--'"

What version of the product are you using? On what operating system?
libwebp 0.3.1 on OSX 10.8.4.

Original issue reported on code.google.com by shi...@dollbooru.org on 18 Aug 2013 at 1:12

[GoogleCodeExporter]

https://gerrit.chromium.org/gerrit/#/c/66222/ added the option to use stdout 
for dwebp

(dwebp in.webp -o -)

Still some work needed for cwebp in/out and dwebp in, though.

Original comment by pascal.m...@gmail.com on 20 Aug 2013 at 1:28

[GoogleCodeExporter]

https://gerrit.chromium.org/gerrit/#/c/68096/
https://gerrit.chromium.org/gerrit/#/c/68095/
https://gerrit.chromium.org/gerrit/#/c/68094/
https://gerrit.chromium.org/gerrit/#/c/68093/

These have all been merged:
7f9de0b Merge changes I994a5587,I8467bb71,I13b50688,I1e2c9c7b
5459030 gif2webp: let -- stop parameter parsing
a4b0aa0 vwebp: let -- stop parameter parsing
98af68f cwebp: let -- stop parameter parsing
a33831e dwebp: let -- stop parameter parsing

Just webpmux left. These will then be available in binary form in the next 
release.

Original comment by jz...@google.com on 18 Dec 2013 at 4:24

• Changed state: Started

[GoogleCodeExporter]

https://gerrit.chromium.org/gerrit/#/c/68180/
b4fa0a4 webpmux: let -- stop parameter parsing

All the examples support this behavior now.

Original comment by jz...@google.com on 19 Dec 2013 at 8:48

• Changed state: Fixed

[GoogleCodeExporter]

Issue 181 has been merged into this issue.

Original comment by jz...@google.com on 7 Jan 2014 at 8:50