Transition to pulling open-vcdiff from repository, instead of using snapshot...

sdch/open_vcdiff/depot/opensource/open-vcdiff/README

-open-vcdiff is an encoder and decoder for the VCDIFF format, as described in
-RFC 3284 : The VCDIFF Generic Differencing and Compression Data Format
-(http://www.ietf.org/rfc/rfc3284.txt)
-A library with a simple API is included, as well as a command-line executable
-that can apply the encoder and decoder to source, target, and delta files.
-For further details, please refer to:
-http://code.google.com/p/open-vcdiff/wiki/HowToUseOpenVcdiff
-
-See INSTALL for (generic) installation instructions for C++: basically
-   ./configure && make && make install
-
-This should compile the unit tests as well as "vcdiff", a simple command-line
-utility to run the encoder and decoder.  Typical usage of vcdiff is as follows
-(the "<" and ">" are file redirect operations, not optional arguments):
-   vcdiff encode -dictionary file.dict < target_file > delta_file
-   vcdiff decode -dictionary file.dict < delta_file > target_file
-To see the command-line syntax of vcdiff, use "vcdiff --help" or just "vcdiff".
-
-To call the encoder from C++ code, assuming that dictionary, target, and delta
-are all std::string objects:
-#include <google/vcencoder.h>  // Read this file for interface details
-[...]
-  open_vcdiff::VCDiffEncoder encoder(dictionary.data(), dictionary.size());
-  encoder.SetFormatFlags(open_vcdiff::VCD_FORMAT_INTERLEAVED);
-  encoder.Encode(target.data(), target.size(), &delta);
-
-Calling the decoder is just as simple:
-#include <google/vcdecoder.h>  // Read this file for interface details
-[...]
-  open_vcdiff::VCDiffDecoder decoder;
-  decoder.Decode(dictionary.data(), dictionary.size(), delta, &target);
-
-When using the encoder, the C++ application must be linked with the library
-options -lvcdcom and -lvcdenc; when using the decoder, it must be linked with
--lvcdcom and -lvcddec.
-
-To verify that the package works on your system, especially after making
-modifications to the source code, please run the unit tests using
-   make check
-
-For further details, please refer to:
-http://code.google.com/p/open-vcdiff/wiki/HowToUseOpenVcdiff
-