Certain protobuf comments could generate invalid C comments
and inadvertently close the comment block. This commit removes '/'
signs in such comments.

One example of a .proto file containing such comments is a commonly
included descriptor.proto from the protobuf library.

Check for NULL pointer for repeated fields passed to protobuf_c_message_free_unpacked

Closes #177

Check for NULL message pointer passed to protobuf_c_message_free_unpacked

Closes #177

warning: assigning to 'uint8_t *' (aka 'unsigned char *')
from 'char *' converts between pointers to integer types
with different sign [-Wpointer-sign]

Add test cases for parsing multiple fields of the same oneof from the wire
Add more tests for submessage merging, including oneofs

Add a field flag and functions to pack/unpack oneofs
Add logic to parse multiple fields for the same oneof
Add logic for merging submessages that contain oneofs

Ironically, we need to tell automake to distribute the CMakeLists.txt
file in the tarball...

For certain platforms where autotools is not the preferred build system,
provide a fallback cmake file that can compile protoc-c and a static
library of libprotobuf-c.

Based on the file from alex85k's protobuf-c repository.

(Issue #168.)

The object file name is not what is expected when building with
automake's "subdir-objects" option. Rather than expecting automake to
generate a specific filename, we simply make the generated header a
dependency of all objects for cxx-generate-packed-data.

(Issue #156, #169.)

Per http://msdn.microsoft.com/en-us/library/z8y1yy88(v=vs.71).aspx,
Microsoft compilers do not support the Standard C keyword 'inline',
instead preferring the implementation-specific '__inline', so add a
workaround for these specific compilers.

Based on a patch from alex85k (#167).

Per the protobuf developers,

    We will from everything away from Google Code eventually. We haven't
    decided where to put future release packages yet but as it seems github
    supports this well chances are we'll use github as the canonical location
    for all downloads.

Build with the latest protobuf release, in preparation for adding
"oneof" support.

gcc silently treats arithmetic on a void pointer as char pointer
arithmetic without -pedantic. Other compilers do not. Make it explicit
that we are doing arithmetic on a pointer with object size 1.

This eliminates the following diagnostic:

    protobuf-c/protobuf-c.c: In function 'parse_packed_repeated_member':
    protobuf-c/protobuf-c.c:2404:34: warning: pointer of type 'void *' used in arithmetic [-Wpedantic]
      void *array = *(void **) member + siz * (*p_n);

(I did not find any other instances of 'void *' arithmetic when
compiling with -pedantic.)

Based on a patch from alex85k (#167).