* add check for reserved keywords in extensions
* add all reserved keywords
* use string without std::
* add test and update name in lite version
* test updates
GeneratedMessageV3#setUnknownFieldsProto3 was trying to delegate to
setUnknownFields but was inadvertently resulting in infinite recursion.
This commit makes setUnknownFields and setUnknownFieldsProto3 delegate
to a common private method to fix the problem and avoid confusion.
* Down-integrate internal changes to github.
* fix python conformance test
* fix csharp conformance test
* add back java map_lite_test.proto's optimize for option
* fix php conformance test
1. Fix C++ tests.
* Add missing files to Makefile.am and fix distcheck in tests.sh
* Remove BUILT_SOURCES from conformance/Makefile.am.
* Add some missing override keyword.
* Add a type cast to int64 because our StrCat() in stubs can't handle size_t.
2. Fix Java tests.
* Add missing test dependency on guava in pom.xml.
* Include newly referenced test data in test resources.
* Manually fix map_lite_test.proto which is overwritten because it's mapped
from map_test.proto in google3.
* Add back "optimize_for = LITE_RUNTIME" which is still needed to keep the
opensource test passing as it's still running lite tests.
* Add a type cast in newBuilder() because without it the code doesn't compile
with openjdk javac 1.8 (the compiler can't figure if it's the right type
due to complex generic typing).
3. Fix Python tests.
* Remove/replace references to <hash_map>.
* Suppress more warnings in setup.py.
* Replace incorrect header inclusion for google/protobuf/proto_api.h.
* Add strings::EndsWith to google/protobuf/stubs/strutil.h because it's
referenced in the updated python C extension code.
* Replace proto2 with google::protobuf. The proto2 name is leaked to
opensource because we removed the subsitition rule for proto2 namespace
but only fixed C++ source code and forgot to update python C extension code.
