Throw an exception when a developer tries to redefine object instantiation
Object engine differ
Only convert test suite result code into valid exit code

As stated in
https://github.com/phpspec/phpspec/pull/317/files#r16391975,
only the RunCommand requires to convert result code.
Merge pull request #480 from gquemener/improvement/run-exit-code

Only convert test suite result code into valid exit code
Fixing confused typehints
Merge pull request #479 from ciaranmcnulty/feature-object-differ

Object engine differ using sebastianbergmann/exporter
Merge pull request #475 from ciaranmcnulty/feature-guard-constructor-redefinition

Throw an exception on redefined object instantiation
Initial working POSIX implementation
Passthru ReRunner for when pcntl is unavailable