Class CheckContext

Provides a context for configure tests. Defines how a test writes to the
screen and log file.

A typical test is just a callable with an instance of CheckContext as
first argument:

def CheckCustom(context, ...)
context.Message('Checking my weird test ... ')
ret = myWeirdTestFunction(...)
context.Result(ret)

Often, myWeirdTestFunction will be one of
context.TryCompile/context.TryLink/context.TryRun. The results of
those are cached, for they are only rebuild, if the dependencies have
changed.

Constructor. Pass the corresponding SConf instance.

Inform about what we are doing right now, e.g.
'Checking for SOMETHING ... '

Inform about the result of the test. res may be an integer or a
string. In case of an integer, the written text will be 'ok' or
'failed'.
The result is only displayed when self.did_show_result is not set.