Don't try to print expected/actual values when they can't be stringified

--HG--
branch : se/dev/native-tests

Set up definitions for try/catch when exception support is disabled

Merge pull request unittest-cpp#143 from unittest-cpp/v2-prep

v2.0.0 prep

Closes unittest-cpp#96

Merge pull request unittest-cpp#111 from unittest-cpp/v1.6.1-prep

v1.6.1 prep

Update docs, versions for 1.6.0.

Prepare v1.5.1 tag

Prepare v1.5.0 tag.

Tagging v1.4 as previously released on sourceforge.