GVariant Database

 * Copied from https://git.gnome.org/browse/gvdb commit a6f0eadb51aae5351a0cfd6b9da3dcba6b134e1a
 * Removed G_GNUC_INTERNAL and GVDB_GNUC_WEAK
 * Fix -Wsign-compare
 * Add clang ifdef guards (#ifndef __clang_analyzer__) around:
   - file_builder_allocate_for_hash
   - file_builder_add_hash
 * Removed G_FILE_CREATE_REPLACE_DESTINATION in gvdb_table_write_contents_async
 * Fix valgrind warnings (gvdb#2)
