protobuf-c/protobuf-c.c: add functionality to merge multiple instances
of the same field on the wire (Fixes #91)
t/generated-code2/test-generated-code2.c: add a test case for merging
messages
t/test-full.proto: expand message definitions to test for merging nested
messages
t/generated-code2/test-generated-code2.c: Rename test_optional_merge to
test_field_merge
ChangeLog: Issue #91