avro

AVRO-474. C: Add source package target to CMake build files

The CMake build scripts can now produce a source tarball, via CPack.
After running cmake in your build directory, "make package_source" will
produce the source tarball.  The only caveat is that CPack doesn't try
to be smart about what to include in the tarball; basically anything in
the top-level source directory is included.  I've added some ignore
patterns to keep out some of the obvious riff-raff like backup files,
and the CMake build directory.  But to produce a truly pristine source
tarball, you should make sure to keep the source directory itself
pristine.


git-svn-id: https://svn.apache.org/repos/asf/avro/trunk@1183643 13f79535-47bb-0310-9956-ffa450edef68